Nalini Pandit’s essay – Ambedkar and the Bhagawat Gita – in Economic and Political Weekly, Vol. 27, No. 20/21 (May 16-23, 1992), pp. 1063-1065, digitized by JSTOR, which is making rounds on the net, makes an interesting reading. Mine own ‘Mundane distortions in the Divine discourse’ dealing with the interpolations in Bhagvad-Gita, accessible in the perspectives on this site, affords the readers an alternate view point to Ambedkar’s point of view as follows.
 
In Nalini Pandit’s essay, it is articulated thus: When emperor Ashoka embraced Buddhism, it became a state religion. The Brahmins, then, lost all state patronage and were reduced to a secondary position. Ashoka prohibited all animal sacrifices in his kingdom. The Brahmins who officiated at these sacrifices lost their chief source of income. Consequently a rebellion of Brahmins against the Buddhist state took place under Pushyamitra Sung who came from a Brahmin dynasty. Pushyamitra destroyed the Buddhist state and established in its place a Brahmin political order. This is what Ambedkar calls a counter-revolution. The Brahmin rulers made Brahmins a class of privileged persons and the varna was turned into caste. The Brahmins brought about a system of graded inequality based on birth. Inter-caste dining and marriages were prohibited. The position of women and shudras was degraded. Manu smriti lays down the laws of this counter-revolution. And the Bhagwat Gita is meant to defend the new social order and its religious dogmas on philosophic grounds.

The soul of the Bhagwat Gita, according to Ambedkar, seems to be the defence of chataturvarnyaan and securing its observance in practice. Krishna does not merely rest content with saying that chatur-varnya is based on guna-karma but he goes further and issues two positive injunctions. The first injunction is contained in chapter 111, verse 26. In this Krishna says that a wise man should not by counter-propaganda create a doubt in the mind of an ignorant person who is a follower of karma kand which, of course, includes the observance of the rules of chaturvarnya. In other words, you must not agitate or excite people to rise in rebellion against the theory of karma kand and all that it includes. The second in-junction is laid down in chapter XVIII, verses 41-48. In this Krishna tells that everyone should do the duty prescribed for his varna and no other and warns that those who worship him and are his devotees will not obtain salvation by mere devotion but by devotion accompanied by observance of duty laid down for his varna. In short a shudra however great he may be as a devotee will not get salvation if he has transgressed the duty of the shudra, namely, to live and die in the services of the higher classes.

As elaborated in Nalini Pandit’s essay, Ambedkar shared D.D. Kosambi’s view that Bhagvad Gita was composed in the reign of the Gupta king Baladitya, who ascended the throne in the year AD 467, to serve the above cited purpose. On the other hand, it is the general belief that the Gita is two millennia old, albeit with some interpolations (variously speculated by many a critic) making their way in between. It would be interesting to see Ambedkar’s view that Bhagvad Gita ‘seems to be the defence of chataturvarnyaan and securing its observance in practice. Krishna does not merely rest content with saying that chatur-varnya is based on guna-karma but he goes further and issues two positive injunctions,’ in the context of the arguments advanced in my said  ‘Mundane distortions in the Divine discourse’. 

About the above cited first injunction contained in chapter 111, verse 26, if v9 to v18 and v24 of the chapter are taken as interpolations, then the said injunction would be an altogether different proposition. And this can be seen in ‘Theory of Action: Bhagvad Gita  Chaper 3’ as rendered by me in this site. 

In so far as the second injunction laid down in chapter XVIII, verses 41-48, in the said ‘Mundane distortions in the Divine discourse’ it is stated that ‘S41- s48 that describe the allotted duties of man on the basis of his caste are clearly interpolations. In essence, the discourse till s40 is about the human nature and how it affects man. As can be seen, the duties on caste lines detailed in the said interpolations have no continuity of argument. As in earlier chapters, the text acquires continuity if only these verses are bypassed as can be seen from 'Thy Looking Glass Bhagvad-Gita Chapter 18’.

Going by the above, the moot point is whether the soul of the Bhagwat Gita is to be found in ‘the defence of chataturvarnyaan and securing its observance in practice’ as opined by Ambedkar, or was it a case of a pollution of a pre-existing text to serve the said cause, which when the discourse is seen in its totality, seems more likely to my mind.