DN 2 conclusively details: What is rūpa (form), and a-rūpa in four jhānas context?

First, it's important to note that of the 34 suttas in DN collection,

around half or more than half of those 34 all use the same model as DN 2 for the samadhi and enlightenment section with 6 higher knowledges (the other DN suttas are heavily elided and not easy to  notice the DN 2 samadhi section is embedded). 

DN-2-SMD

I'll refer to DN 2 samadhi sequence in the rest of the article as DN-2-SMD

The extremely high occurrence of this passage means that the DN-2-SMD sequence from the 7 awakening factor to 6 higher knowledge sequence is not an anomaly, but what the monks preserving the EBT for thousands of years established as the definitive standard.

There are a few strange things different about this sutta from the rest of the pali suttas, that I was puzzled by for a long time. Especially the part where instead of the standard 6 higher knowledges, DN-2-SMD has 8 higher knowledges. 

 Why?

The two new sections don't add something that isn't already present in other suttas.

Then after careful study of those two sections, I realized the answer

Those two sections, which we'll look at in detail now, give a definitive dictionary definition for what  rūpa (form), and a-rūpa means in four jhānas context. 

 DN 2 section on samādhi

(links to full pali+eng. sutta)

• 4.3.2. undistractible-lucidity
• 4.3.2.1. Sense Restraint
• 4.3.2.2. rememberfulness and lucid-discerning
• 4.3.2.3. Contentment
• 4.3.2.4. Giving Up the Hindrances
  • (similes for removing 5niv)
• (7sb awakening factors)
• 4.3.2.5. First jhāna
• 4.3.2.6. Second jhāna
• 4.3.2.7. Third jhāna
• 4.3.2.8. Fourth jhāna
• 4.3.3. The Eight Knowledges
• 4.3.3.1. Knowledge and Vision
  • (simile for knowledge and vision)
• 4.3.3.2. Mind-Made Body
  • (simile for mind made body)
• 4.3.3.3. Psychic Powers
  • (simile for psychic powers)
• 4.3.3.4. Clairaudience
• 4.3.3.5. Comprehending the Minds of Others
• 4.3.3.6. Recollection of Past Lives
• 4.3.3.7. Clairvoyance
• 4.3.3.8. Ending of Defilements

One more important thing to note about DN-2-SMD

The four jhanas and their similes occur where samadhi sambojjhanga is slotted in the section preceding the jhanas. In other words, what DN-2-SMD is saying is that the four jhanas are equivalent to samadhi awakening factor.

Then, in the section with 8 higher knowledges, that occurs where equanimous observation awakening factor happens. 

(7sb awakening factors)

(7sb → 1-3 🐘💭🕵️🏹) Tassime pañca nīvaraṇe pahīne attani samanupassato	(7sb → 1-3 🐘💭🕵️🏹) Seeing that the hindrances have been given up in them,
pā-mojjaṃ jāyati,	virtuous-mirth is born.
(7sb → 4. 😁) pa-muditassa pīti jāyati,	(7sb → 4. 😁) (For one with) virtuous-mirth rapture (is) born.
(7sb → 5. 🌊) pīti-manassa kāyo passambhati,	(7sb → 5. 🌊) (with) en-raptured-mind (the) body (is) pacified.
(7sb → 5.5 🙂) passaddha-kāyo sukhaṃ vedeti,	(7sb → 5.5 🙂) (with) pacified-body, {they experience} pleasure.
(7sb → 6. 🌄) sukhino cittaṃ samādhiyati.	(7sb → 6. 🌄) (For one in) pleasure, (the) mind becomes undistractible-&-lucid.

4.3.2.5. Paṭhamajhāna	4.3.2.5. First jhāna
🚫💑 so vivicc’eva kāmehi	🚫💑 Quite-withdrawn (from) sensuality,
🚫😠 vivicca a-kusalehi dhammehi	🚫😠 withdrawn (from) un-skillful Dhamma [teachings & qualities],

... (and the remaining four jhanas and similes)...

Now we see kāya and rūpa in four jhānas is referring to anatomical 31 body parts and 4 elements

4.3.3. Aṭṭhañāṇa	4.3.3. The Eight Knowledges
4.3.3.1. Vipassanāñāṇa	4.3.3.1. Knowledge and Vision

j4🌕 āneñja⚡ Imperturbabilty is equivalent to 4ip 🌕⚡

“so evaṃ samāhite citte	“When my undistractible-&-lucid mind
parisuddhe pariyodāte	(was thus) purified, bright,
an-aṅgaṇe vigat-ūpak-kilese	Un-blemished, rid-of-defilement,
Mudu-bhūte kammaniye	malleable, wieldy,
ṭhite āneñjap-patte	steady, {attained-to}-imperturbability,

ñāṇadassanāya cittaṃ abhinīharati abhininnāmeti.	—they extend it and project it toward knowledge and vision.
So evaṃ pajānāti:	They understand:
‘ayaṃ kho me kāyo rūpī	‘This body of mine is physical.
cātu-mahā-bhūtiko	It’s made up of the four primary elements,
mātā-pettika-sambhavo	produced by mother and father,
odana-kummās-ūpacayo	built up from rice and porridge,
anicc-ucchādana-parimaddana--	liable to impermanence,-- to wearing away -- and erosion,
--bhedana-viddhaṃsana-dhammo	-- to breaking up -- and destruction.
idañca pana me viññāṇaṃ ettha sitaṃ ettha paṭibaddhan’ti.	And this consciousness of mine is attached to it, tied to it.’

The part about 'produced by mother and father' is also significant.

Because when  VRJ🐍 (V)isuddhi-magga (Re)-definition of (J)hana tries to claim that the body and rupa awareness disappears in the four jhanas, they do so by redefining kaya as a 'body of only mental factors devoid of anatomical body', and the redefine 'rupa' as a visual kasina image composed of 4 elements, rather than the 4 elements of the anatomical body.

Then the next part where consciousness (vinnana) binds to rupa and kaya, obviously it must be the nama and rupa composed of 4 elements and 31 body parts, because vinnana is binding to a living being, not a visual only kasina.

The other bonus higher knowledge also uses kaya and rupa to give them definitive context unequivocally referring to anatomical body

4.3.3.2. Manomayiddhiñāṇa	4.3.3.2. Mind-Made Body

j4🌕 āneñja⚡ Imperturbabilty is equivalent to 4ip 🌕⚡

“so evaṃ samāhite citte	“When my undistractible-&-lucid mind
parisuddhe pariyodāte	(was thus) purified, bright,
an-aṅgaṇe vigat-ūpak-kilese	Un-blemished, rid-of-defilement,
Mudu-bhūte kammaniye	malleable, wieldy,
ṭhite āneñjap-patte	steady, {attained-to}-imperturbability,

manomayaṃ kāyaṃ abhinimmānāya cittaṃ abhinīharati abhininnāmeti.	—they extend it and project it toward the creation of a mind-made body.
So imamhā kāyā aññaṃ kāyaṃ abhinimmināti rūpiṃ manomayaṃ sabbaṅgapaccaṅgiṃ ahīnindriyaṃ.	From this body they create another body, physical, mind-made, complete in all its various parts, not deficient in any faculty.

Again, see how the body and rupa body form is contrasted against citta and mano. If you try to plug in Visuddhimagga redefined kaya as 'collection of mental aggregates', and rupa as 'four elements that compose a visual only kasina', this passage becomes completely incoherent. 

So two things they did to make it impossible for   VRJ🐍 (V)isuddhi-magga (Re)-definition of (J)hana  to corrupt the meaning of 'kaya' and 'rupa':

1.Again, what this section is talking about is making a clone of the whole living being with 31 body parts, so it can't be talking about a visual only kasina and a 'body of only mental factors'. 

2. kaya and rupa are being contrasted against 'mano' and 'citta'. If you use the VRJ redefined 'kaya' and 'rupa', 'body of mental factors' wouldn't be  a contrast with the mind (that is made of mental factors)!

Conclusion

What becomes very clear is that somewhere in the history of Theravada there was a movement to redefine the jhanas into a formless attainment. DN-2-SMD, with its two extra higher knowledges, is carefully constructed to explicitly spell out what rūpa and kāya are, from within the attainment of imperturbable version of fourth jhāna.

In the detailed audit here: VRJ🐍 , 

I show how Vism. tries to swap out rūpa and kāya with their redefinitions, like a crooked casino dealer slipping in hidden cards. 

Unfortunately, this isn't the old west, where crooked dealers would be dealt with swiftly using lethal  frontier justice.

In modern times, slick talking prevarication, obfuscation and sophistry is admired as if it was genuine wisdom. Religious followers are gullible, and through unfortunate circumstance, this VRJ🐍  version of 'Theravada jhāna' became the accepted standard.

So where do we go from here?

The rest depends on you. The EBT preservationists of ancient times did a phenomenal job making it clear what 'rupa' and 'kaya' are.

If you blindly follow teachers who teach VRJ🐍 , then nothing changes.