user254: Wikipedia's Bhavacakra (Within the Theravada tradition) article includes this picture of the wheel:

From inner to outer, it has four rings:

Past, Present, Future
Active and Passive
?
Twelve Nidanas

My question is, what's the third ring? Assuming I know approximately what each word in the third ring means, why are those words in particular placed in those segment of the third ring? What's the relation between the third ring and the other rings? What is the lesson or advice, how is understanding this ring useful/usable towards enlightenment?

user295: Craving, attachment in the present lead to becoming and fabrication due to ignorance. Ignorance is included and if it is not present there is no craving and clinging to feelings hence no fabrication.
What is subjected to birth decay and death (in the future) is a being composed of the 5 aggregates due to fabrication and ignorance in the present.
Craving, clinging in the past due to ignorance hence leading to becoming and fabrication creates the rebirth, mind and matter, 6 sense bases, contact and feeling in the present.

user2282: It's not to be looked at ring by ring but slice by slice so that the components in the inner rings can be combined with those in the outer to complete the picture. According to the Pali exegetical tradition, Dependent Orginination can be looked at in 2 ways (ref: "Connected Discourses" - NidanaSamyutta - Bhikkhu Bodhi):

3 Periods/12 Factors: 3 slices - 1st, 2nd, and 4th rings
Ex: Past life slice: 1st ring: Past; 2nd ring: Active side; 4th ring: Avijja and Sankhara
   Present life slice: 1st ring: Present; 2nd ring: Active+Passive sides; 4th ring: Vinnana, NamaRupa, Salayatana, Phassa, Vedana, Tanha, Upadana, and Bhava;
   Future life slice: 1st ring: Future; 2nd ring: Passive side; 4th ring: Jati and Jara-Marana;
20 Modes/4 Groups: 5 past causes, 5 present effects, 5 present causes, 5 future effects - 4 slices - all rings combined.
Ex: 5 past causes: 1st ring: Past; 2nd ring: Active side; 3rd + 4th rings: Avijja, Sankhara, Tanha, Upadana, and Bhava.
   5 present effects: 1st ring: Present; 2nd ring: Passive;3rd ring is empty; 4th righ: Vinnana, NamaRupa, Salyatana, Phassa, and Vedana
   etc...


user8157: The third ring appears to be stating: (a) the five aggregates are 'passive' or 'neutral' (per the Khandha Sutta, which describes neutral/mere/pure aggregates versus defiled aggregates subjected to clinging) & (b) it is the activity of ignorance, sankhara, craving, attachment & becoming that actively keep the 'wheel of life' spinning. 
This two-fold distinction of the illustrator is based on the premise that 'birth' & 'aging-&-death' refer to physical birth & aging-&-death (rather than psychological 'birth' & 'aging-&-death'). 
It is also based on the premise than 'sankhara' refers to 'volitional formations' (rather than the kaya, vaci & citta sankhara as described in MN 44).
It also appears to infer the 3rd to 7th links are not 'activated' or 'disturbed' by ignorance.  

254: <p>Wikipedia's <a href="https://en.wikipedia.org/wiki/Bhavacakra#Within_the_Theravada_tradition" rel="nofollow noreferrer">Bhavacakra (Within the Theravada tradition)</a> article includes <a href="https://en.wikipedia.org/wiki/Bhavacakra#/media/File:Paticca-Samuppada.JPG" rel="nofollow noreferrer">this picture</a> of the wheel:</p>

<p><a href="https://i.stack.imgur.com/as6GW.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/as6GW.jpg" alt="enter image description here"></a></p>

<p>From inner to outer, it has four rings:</p>

<ol>
<li>Past, Present, Future</li>
<li>Active and Passive</li>
<li>?</li>
<li>Twelve Nidanas</li>
</ol>

<p>My question is, what's the third ring? Assuming I know approximately what each word in the third ring means, why are those words in particular placed in those segment of the third ring? What's the relation between the third ring and the other rings? What is the lesson or advice, how is understanding this ring useful/usable towards enlightenment?</p>
 295: <p>Craving, attachment in the present lead to becoming and fabrication due to ignorance. Ignorance is included and if it is not present there is no craving and clinging to feelings hence no fabrication.</p>

<p>What is subjected to birth decay and death (in the future) is a being composed of the 5 aggregates due to fabrication and ignorance in the present.</p>

<p>Craving, clinging in the past due to ignorance hence leading to becoming and fabrication creates the rebirth, mind and matter, 6 sense bases, contact and feeling in the present.</p>
 2282: <p>It's not to be looked at ring by ring but slice by slice so that the components in the inner rings can be combined with those in the outer to complete the picture. According to the Pali exegetical tradition, Dependent Orginination can be looked at in 2 ways (ref: "Connected Discourses" - NidanaSamyutta - Bhikkhu Bodhi):</p>

<ol>
<li><p>3 Periods/12 Factors: 3 slices - 1st, 2nd, and 4th rings<br/>
Ex: <br/>Past life slice: 1st ring: Past; 2nd ring: Active side; 4th ring: Avijja and Sankhara<br/>
   Present life slice: 1st ring: Present; 2nd ring: Active+Passive sides; 4th ring: Vinnana, NamaRupa, Salayatana, Phassa, Vedana, Tanha, Upadana, and Bhava;<br/>
   Future life slice: 1st ring: Future; 2nd ring: Passive side; 4th ring: Jati and Jara-Marana;</p></li>
<li><p>20 Modes/4 Groups: 5 past causes, 5 present effects, 5 present causes, 5 future effects - 4 slices - all rings combined.<br/>
Ex: <br/>5 past causes: 1st ring: Past; 2nd ring: Active side; 3rd + 4th rings: Avijja, Sankhara, Tanha, Upadana, and Bhava.
   <br/>5 present effects: 1st ring: Present; 2nd ring: Passive;3rd ring is empty; 4th righ: Vinnana, NamaRupa, Salyatana, Phassa, and Vedana
   <br/>etc...</p></li>
</ol>
 8157: <p>The third ring appears to be stating: (a) the five aggregates are 'passive' or 'neutral' (per the <a href="http://www.accesstoinsight.org/tipitaka/sn/sn22/sn22.048.than.html" rel="nofollow">Khandha Sutta</a>, which describes neutral/mere/pure aggregates versus defiled aggregates subjected to clinging) &amp; (b) it is the activity of ignorance, sankhara, craving, attachment &amp; becoming that actively keep the 'wheel of life' spinning. </p>

<p>This two-fold distinction of the illustrator is based on the premise that 'birth' &amp; 'aging-&amp;-death' refer to physical birth &amp; aging-&amp;-death (rather than psychological 'birth' &amp; 'aging-&amp;-death'). </p>

<p>It is also based on the premise than 'sankhara' refers to 'volitional formations' (rather than the kaya, vaci &amp; citta sankhara as described in MN 44).</p>

<p>It also appears to infer the 3rd to 7th links are not 'activated' or 'disturbed' by ignorance.  </p>
