Did Ambedkar think caste was essential to Hinduism, or a distortion of it?
He came, painfully and over many years, to the view that caste was not an abuse that had crept into Hinduism but something the religion's own authoritative texts commanded. This is the pivot of Annihilation of Caste. Many reformers of his day held that caste was a social corruption the true religion did not sanction, and that education and goodwill could remove it while leaving the faith intact. Ambedkar disagreed, and the disagreement is what set him apart.
His argument was that the ordinary Hindu observes caste not from mere habit but because he believes it is enjoined by scripture, and that no amount of appeal to reason or kindness will shift a practice the believer holds to be religiously commanded. Reform, therefore, could not stop at custom. It would have to confront the authority of the sacred texts themselves — which is why he concluded that the destruction of caste meant the destruction of the religious notion on which it rested, and why so many found the argument unbearable.
This is the reasoning that eventually led him out of Hinduism altogether. If the graded order was written into the scriptures and not merely into the manners of the villages, then trying to reform it from inside was, he decided after twenty years of trying, a labour without an end. Whether he read the texts rightly is disputed by Hindu reformers to this day; that he read them as sanctioning caste, and acted on it, is not.
In the Journey: The speech that was never delivered, 1935–1936