user949: Stephen Batchelor claims in several speeches and books that

Buddha never said the Karma and rebirth theory was true,
it is not important to Buddha's teachings, and
when he was a Gelug monk and asked for support for the Karma and rebirth theory, he didn't get any sufficient answers (despite the fact that Gelug Buddhists tend to focus on scientific methods of acquiring knowledge).

According to Batchelor, the Karma theory was a common worldview in India at the time. Siddhartha Gautama's contemporaries believed in Karma like we believe in the Big Bang theory and evolution. Neither of these theories can be proved or refuted with an affordable effort (in order to prove evolution for yourself, you need substantial knowledge of biology plus systemic thinking skills -- both of which are hard to acquire).
Also, neither of these theories affects the main purpose of Buddhist practice -- to reduce suffering. If tomorrow someone proved the Big Bang theory to be definitely true (or definitely wrong), it wouldn't make most of the people happier/unhappier than before.
However, the question about Karma theory affects the Buddhist practice.
If someone believes in rebirth, then they would spend most of their time meditating and preparing for the next lives. This is not just theory -- in some Buddhist communities advanced members spend almost all their evenings in the Buddhist center and almost every vacation on some retreat. It looks like they don't have their own life apart from this practice.
If someone does not believe in the Karma theory, they will focus on making the best of this life (which may be the only one we get). Buddhist practice is a means to live the one life one has as effectively as possible. Basically, you meditate in the evening in order to better achieve your personal goals during the day.
Is the Karma theory an essential component of Buddha's teaching or not?

user5000: "Buddha never said the Karma and rebirth theory was true"
I don't know if he claimed it to be true or not, but it seems like he spoke about karma and rebirth as being true:

"With his mind thus concentrated, purified, and bright, unblemished, free from defects, pliant, malleable, steady, and attained to imperturbability, he directs and inclines it to knowledge of the recollection of past lives (lit: previous homes). He recollects his manifold past lives, i.e., one birth, two births, three births, four, five, ten, twenty, thirty, forty, fifty, one hundred, one thousand, one hundred thousand, many aeons of cosmic contraction, many aeons of cosmic expansion, many aeons of cosmic contraction and expansion, [recollecting], 'There I had such a name, belonged to such a clan, had such an appearance. Such was my food, such my experience of pleasure and pain, such the end of my life. Passing away from that state, I re-arose there. There too I had such a name, belonged to such a clan, had such an appearance. Such was my food, such my experience of pleasure and pain, such the end of my life. Passing away from that state, I re-arose here.' Thus he recollects his manifold past lives in their modes and details. Just as if a man were to go from his home village to another village, and then from that village to yet another village, and then from that village back to his home village. The thought would occur to him, 'I went from my home village to that village over there. There I stood in such a way, sat in such a way, talked in such a way, and remained silent in such a way. From that village I went to that village over there, and there I stood in such a way, sat in such a way, talked in such a way, and remained silent in such a way. From that village I came back home.' In the same way — with his mind thus concentrated, purified, and bright, unblemished, free from defects, pliant, malleable, steady, and attained to imperturbability — the monk directs and inclines it to knowledge of the recollection of past lives. He recollects his manifold past lives... in their modes and details."*
"With his mind thus concentrated, purified, and bright, unblemished, free from defects, pliant, malleable, steady, and attained to imperturbability, he directs and inclines it to knowledge of the passing away and re-appearance of beings. He sees — by means of the divine eye, purified and surpassing the human — beings passing away and re-appearing, and he discerns how they are inferior and superior, beautiful and ugly, fortunate and unfortunate in accordance with their kamma: 'These beings — who were endowed with bad conduct of body, speech, and mind, who reviled the noble ones, held wrong views and undertook actions under the influence of wrong views — with the break-up of the body, after death, have re-appeared in the plane of deprivation, the bad destination, the lower realms, in hell. But these beings — who were endowed with good conduct of body, speech, and mind, who did not revile the noble ones, who held right views and undertook actions under the influence of right views — with the break-up of the body, after death, have re-appeared in the good destinations, in the heavenly world.' Thus — by means of the divine eye, purified and surpassing the human — he sees beings passing away and re-appearing, and he discerns how they are inferior and superior, beautiful and ugly, fortunate and unfortunate in accordance with their kamma. Just as if there were a tall building in the central square [of a town], and a man with good eyesight standing on top of it were to see people entering a house, leaving it, walking along the street, and sitting in the central square. The thought would occur to him, 'These people are entering a house, leaving it, walking along the streets, and sitting in the central square.' In the same way — with his mind thus concentrated, purified, and bright, unblemished, free from defects, pliant, malleable, steady, and attained to imperturbability — the monk directs and inclines it to knowledge of the passing away and re-appearance of beings. He sees — by means of the divine eye, purified and surpassing the human — beings passing away and re-appearing, and he discerns how they are inferior and superior, beautiful and ugly, fortunate and unfortunate in accordance with their kamma..."*

source: http://www.accesstoinsight.org/tipitaka/dn/dn.02.0.than.html
You can certainly find more suttas that will direct you in the same direction of thinking.
"it is not important to Buddha's teachings"
Correct. You don't have to believe in karma and rebirth to achieve complete liberation from suffering.
The main teaching of the Buddha is to do wholesome actions and meditate to find out the cessation to suffering.
"Siddhartha Gautama's contemporaries believed in Karma like we believe in the Big Bang theory and evolution. Neither of these theories can be proved or refuted with an affordable effort (in order to prove evolution for yourself, you need substantial knowledge of biology plus systemic thinking skills -- both of which are hard to acquire)."
Karma exists. Rebirth exists.
Karma does not exist. Rebirth does not exist.
Karma neither exists nor not exists. Rebirth neither exists nor not exists.
All three statements above are true. All of this can be known and seen.
None of the above statements will ever be possible to be 100 % proven with evidence, only with experience, which, unfortunately, is not easy to pass to others.
"Also, neither of these theories affects the main purpose of Buddhist practice -- to reduce suffering. If tomorrow someone proved the Big Bang theory to be definitely true (or definitely wrong), it wouldn't make most of the people happier/unhappier than before."
Your statement is correct. Belief in kamma and rebirth doesn't ALWAYS reduce suffering. Example is an individual who believes in kamma and rebirth very much, but still does such unwholesome actions to end up in a place of deprivation.
Your statement is not correct. Belief in kamma and rebirth reduce suffering. Example is an individual who believes in kamma and rebirth very much, thus he abstains from doing unwholesome actions and ends up in a place of happiness.
Both statements above are true. All of this can be known and seen.
"If someone does not believe in the Karma theory, they will focus on making the best of this life (which may be the only one we get)."
Again your statement is correct, but it can be incorrect for another.
All of this can be known and seen.

You are looking at a wall that has no visible colors, but you are seeing colors on the wall.
You are searching for answers to questions where all answers are true, untrue, true and untrue, neither true nor untrue.
Either one of these views: true, untrue, true and untrue, neither true nor untrue are conditioned by ignorance.
Knowing that all views are true, untrue, true and untrue, neither true nor untrue is cessation of ignorance. Is cessation of clinging and craving. Is complete cessation of suffering.
"Is the Karma theory an essential component of Buddha's teaching or not?"
Buddhist practice is a means to end suffering.
Karma theory is not needed to achieve liberation from suffering.
Don't bother yourself with questions about karma and/or rebirth. You don't need these answers to achieve the end of suffering.
To achieve the end of suffering you need to meditate and look closely at reality as it really is.
Once you will see reality as it really is in its entirety, you will know the answers to all questions.
EDIT:
Think again before marking my answer as the correct answer:
If you know that reality is that there is no kamma nor rebirth, you are thinking wrongly. If that is the case, you don't know the cause of kamma and rebirth, thus you're subjecting yourself to future suffering.
If you know that reality is that there is kamma and rebirth, you are again thinking wrongly. If that is the case, you don't know the path to the cessation of kamma and rebirth, thus you're subjecting yourself to future suffering.
If you know that reality is that there is neither kamma nor rebirth, and that when there is kamma and rebirth they always arise with a cause, you are thinking correctly. If that is the case, you maybe know the cause of kamma and rebirth and the path leading to their cessation, thus there is a chance you're completely liberated from suffering.
If it is not the last, I again say to you: To achieve the end of suffering you need to meditate and look closely at reality as it really is.

user9861: The theoretical concepts of karma and rebirth are not helpful for the beginner in his or her practice of mindfulness meditation. Early progress is made independently of one's abstract beliefs. The concept of rebirth explains almost nothing about one's personal experience. From a modern point of view, the theory of karma is a theory of learning. The process of learning is very complex and mostly unconscious, making it a lifetime study. Understanding how mindfulness meditation actually works is very difficult. Buddhist literature does not explain karma or rebirth, while taking it for granted. The actual psychological processes of karma and rebirth are very difficult to understand and require very special states of meditation to investigate. Trying to understand the two concepts in superficial terms is a waste of time and a source of unnecessary concern.

user471: From "Kamma: A Study Guide" by Ven. Thanissaro you can find the summary below. Please read the full study guide for the justification.

The doctrine of kamma (karma — action) is one of the Buddha's central
  teachings. There is a modern myth that he simply picked up his ideas
  on kamma from the worldview prevalent in his day, and that they aren't
  really integral to his message. Nothing could be further from the
  truth. Early Buddhists often cited the Buddha's teaching on kamma as
  one of the prime teachings that set him apart from his contemporaries,
  and a study of his teachings on kamma will show that they underlie
  everything else he taught.

From the essay "A Remedy for Despair" by Ven. Bodhi:

As we grope about for a handle to prevent ourselves from plummeting
  down into the pits of despondency, we may find the support we need in
  a theme taught for frequent recollection by the Buddha: "Beings are
  the owners of their kamma, the heirs of their kamma; they are molded,
  formed and upheld by their kamma, and they inherit the results of
  their own good and bad deeds." Often enough this reflection has been
  proposed as a means to help us adjust to the vicissitudes in our
  personal fortunes: to accept gain and loss, success and failure,
  pleasure and pain, with a mind that remains unperturbed. This same
  theme, however, can also serve a wider purpose, offering us succor
  when we contemplate the immeasurably greater suffering in which the
  multitudes of our fellow beings are embroiled.
Confronted with a world that is ridden with conflict, violence,
  exploitation and destruction, we feel compelled to find some way to
  make sense out of their evil consequences, to be able to see in
  calamity and devastation something more than regrettable but senseless
  quirks of fate. The Buddha's teaching on kamma and its fruit gives us
  the key to decipher the otherwise unintelligible stream of events. It
  instructs us to recognize in the diverse fortunes of living beings,
  not caprice or accident, but the operation of a principle of moral
  equilibrium which ensures that ultimately a perfect balance obtains
  between the happiness and suffering beings undergo and the ethical
  quality of their intentional actions.


user111: There is no Buddhism without Karma. Paticcasamuppada (the Law of Dependent Origination) is all about Karma and it's consequences. 
Akiriya-ditthi is the false view or opinion of the inefficacy of action: That neither moral good nor moral evil action have any delayed consequences for anyone.
This wrong view was taught by Pūrana-Kassapa during the time of the Buddha.
Today also there are people like Pūrana Kassapa who spread such views. What is more dangerous is that instead of presenting such views as their own beliefs, they try to present them as the teachings of the Buddha and mislead many who are new to Buddhism. 

user43: Let's keep them separate - karma separate from rebirth.
In my understanding, karma is about subtle latent effects of our actions, that create conditions that influence our future experience. In other words, karma is not magic, it's not a moral retribution law, it's just the normal cause-and-effect - albeit the not-so-obvious part of it. 
IMO, the teaching of skillful action that lead to good results and unskillful action that lead to bad results is a critical key component of Buddha-Dharma, at all levels from the most mundane to the most esoteric. This point cannot be emphasized enough.
As for rebirth, it is my opinion, based on my study of sutras and practice of insight meditation, that it is a metaphor for the continuity of information-causation, used in its primitive form as a skillful mean to create a sense of accountability, and hope, in the beginner student's mind.
Whether it's justifiable to keep using these archaic constructs in our digital age is a question that will probably outlive both of us, so I will not answer it here. My personal choice so far has been to reveal the meanings behind the metaphors in the hope that it will reduce confusion on the student's part. In my experience, authentic Dharma is valuable by itself, without the fairy dust.

user-1: There are two things here that I think are worth to have a clear separation: one is what is recorded of the teachings (and how they are understood), and the other is their significance to the path.
Also, notice I'm mainly writing from the point of view of the Pali Canon texts and from a more traditional reading of it.
Karma and Rebirth and the Buddha
There are many interpretations of what was the Buddha's position on these subjects. Among the ones in that vein are:

that karma and rebirth were simply beliefs of his time that the Buddha also had.

I think one problem with that interpretation is that it's diametrically opposed to the kind of mind and attitude the Buddha displays in the sutras. Take the Cūlahatthipadopama sutta for example. In it, the Buddha points the dangers of making claims that could, in reality, be otherwise. His own claims throughout the many sutras seem to be, virtually at all times, very carefully put.
It's hard to conciliate a teacher who teaches his listeners not to make fragile claims (claims that might be wrong) while doing that himself -- that is, it's hard if we take that teacher as a good one.
Another interpretation goes like:

Karma and rebirth were beliefs of his time, and the Buddha repeated those just as means to point his listeners to a deeper truth, but he himself did not agree with those beliefs.

Proponents of this argument usually say these are examples of the Buddha's "skill in means" or that he refrained from opposing his listeners, since they believe those things anyway.
Others would say that another way of presenting this very same argument is that the Buddha lied -- something that he said is not possible for an arahant to do.
It also raises other kinds of questions. For example, it portrays him hesitating about teaching something that, one would think, is "too shocking" to his listeners. And yet, his most shocking teaching is likely anatta. And in the suttas he never appears to hesitate for a second to "shock" his audience with such declarations.
Additionally, it's not that clear that his audience was so overwhelmingly attached to prior beliefs of karma and rebirth as this argument above seem to imply. What history suggests is that, in his time, different beliefs were very popular. Among them, that there are no good or bad deeds ("no karma" doctrine), and that death is "really, the end". That being the case, these ideas likely weren't that shocking.
It's also important to point out that the Buddha's own teaching of karma and rebirth do not appear to be repetitions of prior beliefs, but seem quite original in their particularities -- (to the point the similarities are just on the name, e.g., "karma").
Karma and Rebirth and the Buddha Dharma
"Also, neither of these theories affects the main purpose of Buddhist practice -- to reduce suffering."
Perhaps they do.
For example, in the Buddha's time, there were proponents of "no karma" doctrine. It seems these people believed that there were no intrinsic consequences to their actions, so they could do whatever they want (bad things included) without concern. That is, indeed, the culmination of the full acceptance and belief of "no life after death" view: that morality is artificial (a social construct, an illusion). The ultimate conclusion, therefore, is that it would be foolish to not take illicit advantages when opportunity presents itself and there's no risk of being caught. And that it's foolish to refrain from getting what one wants, regardless if through immoral means.
With that in mind, take the Buddha's teaching to the Kālāmas, where he used a conservative reasoning to make a point for virtuous behavior. In summary, he found the Kālāmas agreeing that good deeds lead to welfare and that bad deeds lead to harm. Then, he proceed to make his case about a person who does good deeds: 

“This noble disciple, Kālāmas, whose mind is in this way without enmity, without ill will, undefiled, and pure, has won four assurances in this very life.
“The first assurance he has won is this: ‘If there is another world, and if there is the fruit and result of good and bad deeds, it is possible that with the breakup of the body, after death, I will be reborn in a good destination, in a heavenly world.’
“The second assurance he has won is this: ‘If there is no other world, and there is no fruit and result of good and bad deeds, still right here, in this very life, I maintain myself in happiness, without enmity and ill will, free of trouble.
“The third assurance he has won is this: ‘Suppose evil comes to one who does evil. Then, when I have no evil intentions toward anyone, how can suffering afflict me, since I do no evil deed?’
“The fourth assurance he has won is this: ‘Suppose evil does not come to one who does evil. Then right here I see myself purified in both respects.’
-- AN 3.65

Basically, he is saying that doing good has, at least, benefits here in this very life. And if turns out there are intrinsic harmful effects of evil actions, one is safe from them, while one is also at peace if there isn't. And if there is another life after death, the effects of bad actions won't drag one to a suffering realm. So, in essence, being virtuous is a win-win situation.
Notice the Buddha is not asking the Kālāmas to believe rebirth at face value. He is just teaching them to be intelligent with their choices in a situation where they don't have the knowledge to be certain about things they are uncertain.
Another aspect of the belief (or lack) in life after death is concerned with the commitment to the path: to attain Nirvana. A person who believes in the traditional view of samsara (life, death, another life, ... and on and on)  may become lax in the practice, as you pointed out. To tackle this problem, many times in the sutras the Buddha is seen instigating his disciples to train with urgency.  
And that urgency may be developed from the very sight of the possibility that he or she may be reborn again: by understanding how feeble and unsatisfactory our lives are, and the previous ones and the next ones, always subject to suffering, never finally released from it. One of the most inspiring sutras on this matter is the Assu Sutta:

“Long have you (repeatedly) experienced the death of a mother. The tears you have shed over the death of a mother while transmigrating & wandering this long, long time—crying & weeping from being joined with what is displeasing, being separated from what is pleasing—are greater than the water in the four great oceans.
“Long have you (repeatedly) experienced the death of a father… the death of a brother… the death of a sister… the death of a son… the death of a daughter… loss with regard to relatives… loss with regard to wealth… loss with regard to disease. The tears you have shed over loss with regard to disease while transmigrating & wandering this long, long time—crying & weeping from being joined with what is displeasing, being separated from what is pleasing—are greater than the water in the four great oceans.
“Why is that? From an inconstruable beginning comes transmigration. A beginning point is not evident, though beings hindered by ignorance and fettered by craving are transmigrating & wandering on. Long have you thus experienced stress, experienced pain, experienced loss, swelling the cemeteries—enough to become disenchanted with all fabricated things, enough to become dispassionate, enough to be released.”
-- SN 15.3

Finally, to the Buddha (as far as we are talking about what has been recorded about his teachings), fully dedicating the current life to the practice is precisely the best of his recommendation. While he did taught lay people and helped them to maintain their practice (people who were still dedicated to the ordinary life affairs), it is the full commitment that the Buddha praised more -- the abandonment of ordinary affairs of life and full dedication to reach nirvana in this very life.
So, as far as we are talking about what is recorded of what the Buddha said, I don't think they agree with the idea that "Buddhist practice is a means to live the one life one has as effectively as possible. Basically, you meditate in the evening in order to better achieve your personal goals during the day".
It is definitely in agreement that the practice, for whatever extent exercised, have fruits and these are pointed to the "welfare" side of things. But the highest alignment with what the Buddha considered to be "noble" are those who have abandoned all their personal goals, leaving only one remaining: to end suffering.
For more on this theme, see also:

Is rebirth a delusional belief?
Is rebirth/reincarnation central to Buddhism?
Discernment or blind belief?


949: <p><a href="https://en.wikipedia.org/wiki/Stephen_Batchelor_(author)" rel="nofollow noreferrer">Stephen Batchelor</a> claims in several speeches and books that</p>

<ul>
<li>Buddha never said the Karma and rebirth theory was true,</li>
<li>it is not important to Buddha's teachings, and</li>
<li>when he was a Gelug monk and asked for support for the Karma and rebirth theory, he didn't get any sufficient answers (despite the fact that Gelug Buddhists tend to focus on scientific methods of acquiring knowledge).</li>
</ul>

<p>According to Batchelor, the Karma theory was a common worldview in India at the time. Siddhartha Gautama's contemporaries believed in Karma like we believe in the Big Bang theory and evolution. Neither of these theories can be proved or refuted with an affordable effort (in order to prove evolution for yourself, you need substantial knowledge of biology plus systemic thinking skills -- both of which are hard to acquire).</p>

<p>Also, neither of these theories affects the main purpose of Buddhist practice -- to reduce suffering. If tomorrow someone proved the Big Bang theory to be definitely true (or definitely wrong), it wouldn't make most of the people happier/unhappier than before.</p>

<p>However, the question about Karma theory affects the Buddhist practice.</p>

<p>If someone believes in rebirth, then they would spend most of their time meditating and preparing for the next lives. This is not just theory -- in some Buddhist communities advanced members spend almost all their evenings in the Buddhist center and almost every vacation on some retreat. It looks like they don't have their own life apart from this practice.</p>

<p>If someone does not believe in the Karma theory, they will focus on making the best of this life (which may be the only one we get). Buddhist practice is a means to live the one life one has as effectively as possible. Basically, you meditate in the evening in order to better achieve your personal goals during the day.</p>

<p>Is the Karma theory an essential component of Buddha's teaching or not?</p>
 5000: <p><strong>&quot;Buddha never said the Karma and rebirth theory was true&quot;</strong></p>
<p>I don't know if he claimed it to be true or not, but it seems like he spoke about karma and rebirth as being true:</p>
<blockquote>
<p>&quot;With his mind thus concentrated, purified, and bright, unblemished, free from defects, pliant, malleable, steady, and attained to imperturbability, he directs and inclines it to knowledge of the recollection of past lives (lit: previous homes). He recollects his manifold past lives, i.e., one birth, two births, three births, four, five, ten, twenty, thirty, forty, fifty, one hundred, one thousand, one hundred thousand, many aeons of cosmic contraction, many aeons of cosmic expansion, many aeons of cosmic contraction and expansion, [recollecting], 'There I had such a name, belonged to such a clan, had such an appearance. Such was my food, such my experience of pleasure and pain, such the end of my life. Passing away from that state, I re-arose there. There too I had such a name, belonged to such a clan, had such an appearance. Such was my food, such my experience of pleasure and pain, such the end of my life. Passing away from that state, I re-arose here.' Thus he recollects his manifold past lives in their modes and details. Just as if a man were to go from his home village to another village, and then from that village to yet another village, and then from that village back to his home village. The thought would occur to him, 'I went from my home village to that village over there. There I stood in such a way, sat in such a way, talked in such a way, and remained silent in such a way. From that village I went to that village over there, and there I stood in such a way, sat in such a way, talked in such a way, and remained silent in such a way. From that village I came back home.' In the same way — with his mind thus concentrated, purified, and bright, unblemished, free from defects, pliant, malleable, steady, and attained to imperturbability — the monk directs and inclines it to knowledge of the recollection of past lives. He recollects his manifold past lives... in their modes and details.&quot;*</p>
<p>&quot;With his mind thus concentrated, purified, and bright, unblemished, free from defects, pliant, malleable, steady, and attained to imperturbability, he directs and inclines it to knowledge of the passing away and re-appearance of beings. He sees — by means of the divine eye, purified and surpassing the human — beings passing away and re-appearing, and he discerns how they are inferior and superior, beautiful and ugly, fortunate and unfortunate in accordance with their kamma: 'These beings — who were endowed with bad conduct of body, speech, and mind, who reviled the noble ones, held wrong views and undertook actions under the influence of wrong views — with the break-up of the body, after death, have re-appeared in the plane of deprivation, the bad destination, the lower realms, in hell. But these beings — who were endowed with good conduct of body, speech, and mind, who did not revile the noble ones, who held right views and undertook actions under the influence of right views — with the break-up of the body, after death, have re-appeared in the good destinations, in the heavenly world.' Thus — by means of the divine eye, purified and surpassing the human — he sees beings passing away and re-appearing, and he discerns how they are inferior and superior, beautiful and ugly, fortunate and unfortunate in accordance with their kamma. Just as if there were a tall building in the central square [of a town], and a man with good eyesight standing on top of it were to see people entering a house, leaving it, walking along the street, and sitting in the central square. The thought would occur to him, 'These people are entering a house, leaving it, walking along the streets, and sitting in the central square.' In the same way — with his mind thus concentrated, purified, and bright, unblemished, free from defects, pliant, malleable, steady, and attained to imperturbability — the monk directs and inclines it to knowledge of the passing away and re-appearance of beings. He sees — by means of the divine eye, purified and surpassing the human — beings passing away and re-appearing, and he discerns how they are inferior and superior, beautiful and ugly, fortunate and unfortunate in accordance with their kamma...&quot;*</p>
</blockquote>
<p>source: <a href="http://www.accesstoinsight.org/tipitaka/dn/dn.02.0.than.html" rel="nofollow noreferrer">http://www.accesstoinsight.org/tipitaka/dn/dn.02.0.than.html</a></p>
<p>You can certainly find more suttas that will direct you in the same direction of thinking.</p>
<p><strong>&quot;it is not important to Buddha's teachings&quot;</strong></p>
<p>Correct. You don't have to believe in karma and rebirth to achieve complete liberation from suffering.</p>
<p>The main teaching of the Buddha is to do wholesome actions and meditate to find out the cessation to suffering.</p>
<p><strong>&quot;Siddhartha Gautama's contemporaries believed in Karma like we believe in the Big Bang theory and evolution. Neither of these theories can be proved or refuted with an affordable effort (in order to prove evolution for yourself, you need substantial knowledge of biology plus systemic thinking skills -- both of which are hard to acquire).&quot;</strong></p>
<p>Karma exists. Rebirth exists.</p>
<p>Karma does not exist. Rebirth does not exist.</p>
<p>Karma neither exists nor not exists. Rebirth neither exists nor not exists.</p>
<p>All three statements above are true. All of this can be known and seen.</p>
<p>None of the above statements will ever be possible to be 100 % proven with evidence, only with experience, which, unfortunately, is not easy to pass to others.</p>
<p><strong>&quot;Also, neither of these theories affects the main purpose of Buddhist practice -- to reduce suffering. If tomorrow someone proved the Big Bang theory to be definitely true (or definitely wrong), it wouldn't make most of the people happier/unhappier than before.&quot;</strong></p>
<p>Your statement is correct. Belief in kamma and rebirth doesn't ALWAYS reduce suffering. Example is an individual who believes in kamma and rebirth very much, but still does such unwholesome actions to end up in a place of deprivation.</p>
<p>Your statement is not correct. Belief in kamma and rebirth reduce suffering. Example is an individual who believes in kamma and rebirth very much, thus he abstains from doing unwholesome actions and ends up in a place of happiness.</p>
<p>Both statements above are true. All of this can be known and seen.</p>
<p><strong>&quot;If someone does not believe in the Karma theory, they will focus on making the best of this life (which may be the only one we get).&quot;</strong></p>
<p>Again your statement is correct, but it can be incorrect for another.</p>
<p>All of this can be known and seen.</p>
<hr />
<p>You are looking at a wall that has no visible colors, but you are seeing colors on the wall.</p>
<p>You are searching for answers to questions where all answers are true, untrue, true and untrue, neither true nor untrue.</p>
<p>Either one of these views: true, untrue, true and untrue, neither true nor untrue are conditioned by ignorance.</p>
<p>Knowing that all views are true, untrue, true and untrue, neither true nor untrue is cessation of ignorance. Is cessation of clinging and craving. Is complete cessation of suffering.</p>
<p><strong>&quot;Is the Karma theory an essential component of Buddha's teaching or not?&quot;</strong></p>
<p>Buddhist practice is a means to end suffering.</p>
<p>Karma theory is not needed to achieve liberation from suffering.</p>
<p>Don't bother yourself with questions about karma and/or rebirth. You don't need these answers to achieve the end of suffering.</p>
<p>To achieve the end of suffering you need to meditate and look closely at reality as it really is.</p>
<p>Once you will see reality as it really is in its entirety, you will know the answers to all questions.</p>
<p><strong>EDIT:</strong></p>
<p>Think again before marking my answer as the correct answer:</p>
<p>If you know that reality is that there is no kamma nor rebirth, you are thinking wrongly. If that is the case, you don't know the cause of kamma and rebirth, thus you're subjecting yourself to future suffering.</p>
<p>If you know that reality is that there is kamma and rebirth, you are again thinking wrongly. If that is the case, you don't know the path to the cessation of kamma and rebirth, thus you're subjecting yourself to future suffering.</p>
<p>If you know that reality is that there is neither kamma nor rebirth, and that when there is kamma and rebirth they always arise with a cause, you are thinking correctly. If that is the case, you maybe know the cause of kamma and rebirth and the path leading to their cessation, thus there is a chance you're completely liberated from suffering.</p>
<p>If it is not the last, I again say to you: To achieve the end of suffering you need to meditate and look closely at reality as it really is.</p>
 9861: <p>The theoretical concepts of karma and rebirth are not helpful for the beginner in his or her practice of mindfulness meditation. Early progress is made independently of one's abstract beliefs. The concept of rebirth explains almost nothing about one's personal experience. From a modern point of view, the theory of karma is a theory of learning. The process of learning is very complex and mostly unconscious, making it a lifetime study. Understanding how mindfulness meditation actually works is very difficult. Buddhist literature does not explain karma or rebirth, while taking it for granted. The actual psychological processes of karma and rebirth are very difficult to understand and require very special states of meditation to investigate. Trying to understand the two concepts in superficial terms is a waste of time and a source of unnecessary concern.</p>
 471: <p>From "<a href="http://www.accesstoinsight.org/lib/study/kamma.html" rel="nofollow noreferrer">Kamma: A Study Guide</a>" by <a href="https://en.wikipedia.org/wiki/Thanissaro_Bhikkhu" rel="nofollow noreferrer">Ven. Thanissaro</a> you can find the summary below. Please read the full study guide for the justification.</p>

<blockquote>
  <p><strong>The doctrine of kamma (karma — action) is one of the Buddha's central
  teachings.</strong> There is a modern myth that he simply picked up his ideas
  on kamma from the worldview prevalent in his day, and that they aren't
  really integral to his message. Nothing could be further from the
  truth. Early Buddhists often cited the Buddha's teaching on kamma as
  one of the prime teachings that set him apart from his contemporaries,
  and <strong>a study of his teachings on kamma will show that they underlie
  everything else he taught.</strong></p>
</blockquote>

<p>From the essay "<a href="http://www.accesstoinsight.org/lib/authors/bodhi/bps-essay_12.html" rel="nofollow noreferrer">A Remedy for Despair</a>" by <a href="https://en.wikipedia.org/wiki/Bhikkhu_Bodhi" rel="nofollow noreferrer">Ven. Bodhi</a>:</p>

<blockquote>
  <p>As we grope about for a handle to prevent ourselves from plummeting
  down into the pits of despondency, we may find the support we need in
  a theme taught for frequent recollection by the Buddha: "Beings are
  the owners of their kamma, the heirs of their kamma; they are molded,
  formed and upheld by their kamma, and they inherit the results of
  their own good and bad deeds." Often enough this reflection has been
  proposed as a means to help us adjust to the vicissitudes in our
  personal fortunes: to accept gain and loss, success and failure,
  pleasure and pain, with a mind that remains unperturbed. This same
  theme, however, can also serve a wider purpose, offering us succor
  when we contemplate the immeasurably greater suffering in which the
  multitudes of our fellow beings are embroiled.</p>
  
  <p>Confronted with a world that is ridden with conflict, violence,
  exploitation and destruction, we feel compelled to find some way to
  make sense out of their evil consequences, to be able to see in
  calamity and devastation something more than regrettable but senseless
  quirks of fate. <strong>The Buddha's teaching on kamma and its fruit gives us
  the key to decipher the otherwise unintelligible stream of events. It
  instructs us to recognize in the diverse fortunes of living beings,
  not caprice or accident, but the operation of a principle of moral
  equilibrium which ensures that ultimately a perfect balance obtains
  between the happiness and suffering beings undergo and the ethical
  quality of their intentional actions.</strong></p>
</blockquote>
 111: <p>There is no Buddhism without Karma. Paticcasamuppada (the Law of Dependent Origination) is all about Karma and it's consequences. </p>

<p>Akiriya-ditthi is the false view or opinion of the inefficacy of action: That neither moral good nor moral evil action have any delayed consequences for anyone.</p>

<p>This wrong view was taught by <a href="http://www.palikanon.com/english/pali_names/pu/purana_kassapa.htm" rel="nofollow noreferrer">Pūrana-Kassapa</a> during the time of the Buddha.</p>

<p>Today also there are people like Pūrana Kassapa who spread such views. What is more dangerous is that instead of presenting such views as their own beliefs, they try to present them as the teachings of the Buddha and mislead many who are new to Buddhism. </p>
 43: <p>Let's keep them separate - karma separate from rebirth.</p>

<p>In my understanding, karma is about subtle latent effects of our actions, that create conditions that influence our future experience. In other words, karma is not magic, it's not a moral retribution law, it's just the normal cause-and-effect - albeit the not-so-obvious part of it. </p>

<p>IMO, the teaching of skillful action that lead to good results and unskillful action that lead to bad results is a critical key component of Buddha-Dharma, at all levels from the most mundane to the most esoteric. This point cannot be emphasized enough.</p>

<p>As for rebirth, it is my opinion, based on my study of sutras and practice of insight meditation, that it is a metaphor for the continuity of information-causation, used in its primitive form as a skillful mean to create a sense of accountability, and hope, in the beginner student's mind.</p>

<p>Whether it's justifiable to keep using these archaic constructs in our digital age is a question that will probably outlive both of us, so I will not answer it here. My personal choice so far has been to reveal the meanings behind the metaphors in the hope that it will reduce confusion on the student's part. In my experience, authentic Dharma is valuable by itself, without the fairy dust.</p>
 -1: <p>There are two things here that I think are worth to have a clear separation: one is what is recorded of the teachings (and how they are understood), and the other is their significance to the path.</p>

<p>Also, notice I'm mainly writing from the point of view of the Pali Canon texts and from a more traditional reading of it.</p>

<h1>Karma and Rebirth and the Buddha</h1>

<p>There are many interpretations of what was the Buddha's position on these subjects. Among the ones in that vein are:</p>

<ol>
<li>that karma and rebirth were simply beliefs of his time that the Buddha also had.</li>
</ol>

<p>I think one problem with that interpretation is that it's diametrically opposed to the kind of mind and attitude the Buddha displays in the sutras. Take the Cūlahatthipadopama sutta for example. In it, the Buddha points the dangers of making claims that could, in reality, be otherwise. His own claims throughout the many sutras seem to be, virtually at all times, very carefully put.</p>

<p>It's hard to conciliate a teacher who teaches his listeners not to make fragile claims (claims that might be wrong) while doing that himself -- that is, it's hard if we take that teacher as a good one.</p>

<p>Another interpretation goes like:</p>

<ol start="2">
<li>Karma and rebirth were beliefs of his time, and the Buddha repeated those just as means to point his listeners to a deeper truth, but he himself did not agree with those beliefs.</li>
</ol>

<p>Proponents of this argument usually say these are examples of the Buddha's "skill in means" or that he refrained from opposing his listeners, since they believe those things anyway.</p>

<p>Others would say that another way of presenting this very same argument is that the Buddha lied -- something that he said is not possible for an arahant to do.</p>

<p>It also raises other kinds of questions. For example, it portrays him hesitating about teaching something that, one would think, is "too shocking" to his listeners. And yet, his most shocking teaching is likely <em>anatta</em>. And in the suttas he never appears to hesitate for a second to "shock" his audience with such declarations.</p>

<p>Additionally, it's not that clear that his audience was so overwhelmingly attached to prior beliefs of karma and rebirth as this argument above seem to imply. What history suggests is that, in his time, different beliefs were very popular. Among them, that there are no good or bad deeds ("no karma" doctrine), and that death is "really, the end". That being the case, these ideas likely weren't that shocking.</p>

<p>It's also important to point out that the Buddha's own teaching of karma and rebirth do not appear to be repetitions of prior beliefs, but seem quite original in their particularities -- (to the point the similarities are just on the name, e.g., "karma").</p>

<h1>Karma and Rebirth and the Buddha Dharma</h1>

<p><em>"<strong>Also, neither of these theories affects the main purpose of Buddhist practice -- to reduce suffering.</em>"</strong></p>

<p>Perhaps they do.</p>

<p>For example, in the Buddha's time, there were proponents of "no karma" doctrine. It seems these people believed that there were no intrinsic consequences to their actions, so they could do whatever they want (bad things included) without concern. That is, indeed, the culmination of the full acceptance and belief of "no life after death" view: that morality is artificial (a social construct, an illusion). The ultimate conclusion, therefore, is that it would be foolish to not take illicit advantages when opportunity presents itself and there's no risk of being caught. And that it's foolish to refrain from getting what one wants, regardless if through immoral means.</p>

<p>With that in mind, take the Buddha's teaching to the Kālāmas, where he used a conservative reasoning to make a point for virtuous behavior. In summary, he found the Kālāmas agreeing that good deeds lead to welfare and that bad deeds lead to harm. Then, he proceed to make his case about a person who does good deeds: </p>

<blockquote>
  <p>“This noble disciple, Kālāmas, whose mind is in this way without enmity, without ill will, undefiled, and pure, has won four assurances in this very life.</p>
  
  <p>“The first assurance he has won is this: ‘If there is another world, and if there is the fruit and result of good and bad deeds, it is possible that with the breakup of the body, after death, I will be reborn in a good destination, in a heavenly world.’</p>
  
  <p>“The second assurance he has won is this: ‘If there is no other world, and there is no fruit and result of good and bad deeds, still right here, in this very life, I maintain myself in happiness, without enmity and ill will, free of trouble.</p>
  
  <p>“The third assurance he has won is this: ‘Suppose evil comes to one who does evil. Then, when I have no evil intentions toward anyone, how can suffering afflict me, since I do no evil deed?’</p>
  
  <p>“The fourth assurance he has won is this: ‘Suppose evil does not come to one who does evil. Then right here I see myself purified in both respects.’</p>
  
  <p>-- AN 3.65</p>
</blockquote>

<p>Basically, he is saying that doing good has, at least, benefits here in this very life. And if turns out there are intrinsic harmful effects of evil actions, one is safe from them, while one is also at peace if there isn't. And if there is another life after death, the effects of bad actions won't drag one to a suffering realm. So, in essence, being virtuous is a win-win situation.</p>

<p>Notice the Buddha is not asking the Kālāmas to believe rebirth at face value. He is just teaching them to be intelligent with their choices in a situation where they don't have the knowledge to be certain about things they are uncertain.</p>

<p>Another aspect of the belief (or lack) in life after death is concerned with the commitment to the path: to attain Nirvana. A person who believes in the traditional view of samsara (life, death, another life, ... and on and on)  may become lax in the practice, as you pointed out. To tackle this problem, many times in the sutras the Buddha is seen instigating his disciples to train with <em>urgency</em>.  </p>

<p>And that urgency may be developed from the very sight of the possibility that he or she may be reborn again: by understanding how feeble and unsatisfactory our lives are, and the previous ones and the next ones, always subject to suffering, never finally released from it. One of the most inspiring sutras on this matter is the Assu Sutta:</p>

<blockquote>
  <p>“Long have you (repeatedly) experienced the death of a mother. The tears you have shed over the death of a mother while transmigrating &amp; wandering this long, long time—crying &amp; weeping from being joined with what is displeasing, being separated from what is pleasing—are greater than the water in the four great oceans.</p>
  
  <p>“Long have you (repeatedly) experienced the death of a father… the death of a brother… the death of a sister… the death of a son… the death of a daughter… loss with regard to relatives… loss with regard to wealth… loss with regard to disease. The tears you have shed over loss with regard to disease while transmigrating &amp; wandering this long, long time—crying &amp; weeping from being joined with what is displeasing, being separated from what is pleasing—are greater than the water in the four great oceans.</p>
  
  <p>“Why is that? From an inconstruable beginning comes transmigration. A beginning point is not evident, though beings hindered by ignorance and fettered by craving are transmigrating &amp; wandering on. Long have you thus experienced stress, experienced pain, experienced loss, swelling the cemeteries—enough to become disenchanted with all fabricated things, enough to become dispassionate, enough to be released.”</p>
  
  <p>-- <a href="https://suttacentral.net/en/sn15.3" rel="nofollow noreferrer">SN 15.3</a></p>
</blockquote>

<p>Finally, to the Buddha (as far as we are talking about what has been recorded about his teachings), fully dedicating the current life to the practice is precisely the best of his recommendation. While he did taught lay people and helped them to maintain their practice (people who were still dedicated to the ordinary life affairs), it is the full commitment that the Buddha praised more -- the abandonment of ordinary affairs of life and full dedication to reach nirvana in this very life.</p>

<p>So, as far as we are talking about what is recorded of what the Buddha said, I don't think they agree with the idea that "<em>Buddhist practice is a means to live the one life one has as effectively as possible. Basically, you meditate in the evening in order to better achieve your personal goals during the day</em>".</p>

<p>It is definitely in agreement that the practice, for whatever extent exercised, have fruits and these are pointed to the "welfare" side of things. But the highest alignment with what the Buddha considered to be "noble" are those who have abandoned all their personal goals, leaving only one remaining: to end suffering.</p>

<p>For more on this theme, see also:</p>

<ul>
<li><p><a href="https://buddhism.stackexchange.com/q/3420/382">Is rebirth a delusional belief?</a></p></li>
<li><p><a href="https://buddhism.stackexchange.com/q/7098/382">Is rebirth/reincarnation central to Buddhism?</a></p></li>
<li><p><a href="https://buddhism.stackexchange.com/q/20154/382">Discernment or blind belief?</a></p></li>
</ul>
