Deuteronomy 32:18

Of the rock [that] begat thee thou art unmindful
The same with the rock of salvation, ( Deuteronomy 32:15 ) ; repeated and expressed in different words, that their wretched ingratitude might be taken notice of and observed: begetting is ascribed to this rock, as regeneration is to Christ, ( 1 John 2:29 ) ; and was true of some among the Jews: some choose to render the words, "the rock of thy kindred" ^F11; being a near kinsman, a brother through his incarnation, which aggravated their unmindfulness of him:

and hast forgotten God that formed thee:
for the rock they were unmindful of and forgot is the true God and eternal life, the essential Word of God, as both the Targums of Jonathan and Jerusalem interpret it; him the Jewish nation forgot; they forgot the characters given of him in the promises and prophecies of the Old Testament; and therefore they knew him not when he came and fulfilled the voices of the prophets they were ignorant of in condemning him: hence they were unmindful of his person, his offices, his works, his benefits, and the great salvation by him; as indeed too many are that call themselves Christians: some observe that the word here used signifies bringing forth children with pain, and so way respect the bitter sorrows and sufferings of Christ, sometimes expressed by a word ^F12 which signifies the pains of women in childbirth, ( Acts 2:24 ) ; and called the travail of his soul, ( Isaiah 53:11 ) ; and so a further aggravation of their ingratitude, that they should forget him that suffered so much, at least on account of some of them; for, those he endured to bring forth children unto God, or to gather together the children of God, scattered abroad both in Judea and in the whole world, ( John 11:51 John 11:52 ) .