user17744: 
“Here, bhikkhus, some person has a confident mind. Having examined his mind with my mind, I know that if this person were to die at this time, as if carried there he would be placed in heaven. What is the reason for that? It is because his mind is confident. It is because of the mind’s confidence that some beings here, when the body perishes, are reborn after death in a good bourn, in a heavenly world.”
Iti 21

Why we must have a confident mind ? What is a confident mind according to the Lord Buddha ?
What are the differences between confident and

Conceit
Clinging to a view


user-1: 
What is a confident mind according to the Lord Buddha?

From your quote, confidence is translated from the pali word pasannacitta. Pasannacitta literally means devoted mind, and can be interpreted as a person having faith (saddha).
https://www.wisdomlib.org/definition/pasannacitta

Why we must have a confident mind?

It is considered one of the five mental faculties/indryas that aids progression towards enlightenment.
https://www.accesstoinsight.org/tipitaka/sn/sn48/sn48.010.than.html

What are the differences between confident and conceit

Conceit (mana), is a cetasika with attachment/lobha as base. Mana means that we are attached to the misconception that there is a self that is superior to others.

What are the differences between confident and clinging to a view

Primarily the difference is the fruit of their karma. Besides being a mental faculty mentioned above, AN 5.38 also lists five benefits of saddha for laypersons, for instance.
https://www.accesstoinsight.org/tipitaka/an/an05/an05.038.than.html
Clinging to a view, on the other hand is simply not beneficial, and perpetuates dissatisfaction. Your comparison with conceit seems like an appropriate example.

user254: The word in question is pasanna (see dictionary definition here).
I don't know why Ireland translated that as "confident". The other modern translations I'm able to read are Italian, "una mente pura" (meaning a mind that is "pure" or "sinless"), and French, "l'esprit clair" (meaning a mind or spirit that's "clear" or "transparent" or "bright") -- though I beware that any modern language might not have a single word that's an exact translation.
In SN 55.40 there's a word translated "experiential confidence" or "verified confidence" -- that word is aveccappasāda, a compound of pasāda with avecca.
I note that the definitions of pasanna and pasāda are similar.

17744: <blockquote>
<p>“Here, bhikkhus, some person has a confident mind. Having examined his mind with my mind, I know that if this person were to die at this time, as if carried there he would be placed in heaven. What is the reason for that? It is because his mind is confident. It is because of the mind’s confidence that some beings here, when the body perishes, are reborn after death in a good bourn, in a heavenly world.”</p>
<p><a href="https://suttacentral.net/iti21/en/ireland" rel="nofollow noreferrer">Iti 21</a></p>
</blockquote>
<p>Why we must have a confident mind ? What is a confident mind according to the Lord Buddha ?</p>
<p>What are the differences between confident and</p>
<ol>
<li>Conceit</li>
<li>Clinging to a view</li>
</ol>
 -1: <blockquote>
  <p>What is a confident mind according to the Lord Buddha?</p>
</blockquote>

<p>From your quote, confidence is translated from the pali word pasannacitta. Pasannacitta literally means devoted mind, and can be interpreted as a person having faith (saddha).</p>

<p><a href="https://www.wisdomlib.org/definition/pasannacitta" rel="nofollow noreferrer">https://www.wisdomlib.org/definition/pasannacitta</a></p>

<blockquote>
  <p>Why we must have a confident mind?</p>
</blockquote>

<p>It is considered one of the five mental faculties/indryas that aids progression towards enlightenment.</p>

<p><a href="https://www.accesstoinsight.org/tipitaka/sn/sn48/sn48.010.than.html" rel="nofollow noreferrer">https://www.accesstoinsight.org/tipitaka/sn/sn48/sn48.010.than.html</a></p>

<blockquote>
  <p>What are the differences between confident and conceit</p>
</blockquote>

<p>Conceit (mana), is a cetasika with attachment/lobha as base. Mana means that we are attached to the misconception that there is a self that is superior to others.</p>

<blockquote>
  <p>What are the differences between confident and clinging to a view</p>
</blockquote>

<p>Primarily the difference is the fruit of their karma. Besides being a mental faculty mentioned above, AN 5.38 also lists five benefits of saddha for laypersons, for instance.</p>

<p><a href="https://www.accesstoinsight.org/tipitaka/an/an05/an05.038.than.html" rel="nofollow noreferrer">https://www.accesstoinsight.org/tipitaka/an/an05/an05.038.than.html</a></p>

<p>Clinging to a view, on the other hand is simply not beneficial, and perpetuates dissatisfaction. Your comparison with conceit seems like an appropriate example.</p>
 254: <p>The word in question is <em>pasanna</em> (see <a href="https://suttacentral.net/define/pasanna" rel="nofollow noreferrer">dictionary definition here</a>).</p>

<p>I don't know why Ireland translated that as "confident". The other modern translations I'm able to read are Italian, "<em>una mente pura</em>" (meaning a mind that is "pure" or "sinless"), and French, "<em>l'esprit clair</em>" (meaning a mind or spirit that's "clear" or "transparent" or "bright") -- though I beware that any modern language might not have a single word that's an exact translation.</p>

<p>In <a href="https://suttacentral.net/sn55.40/en/sujato" rel="nofollow noreferrer">SN 55.40</a> there's a word translated "experiential confidence" or "verified confidence" -- that word is <a href="https://suttacentral.net/define/aveccappas%C4%81da" rel="nofollow noreferrer">aveccappasāda</a>, a compound of <a href="https://suttacentral.net/define/pas%C4%81da" rel="nofollow noreferrer">pasāda</a> with <a href="https://suttacentral.net/define/avecca" rel="nofollow noreferrer">avecca</a>.</p>

<p>I note that the definitions of <em>pasanna</em> and <em>pasāda</em> are similar.</p>
