You were unmindful of the Rock that bore you, and you forgot the God who gave you birth.
18. Of the Rock Lat., “of the God,” etc. that begat thee. He again aggravates the criminality of the people by referring to their ingratitude, inasmuch as they did not fall through ignorance, but willfully stifled that knowledge of God, which ought to have shone brightly in all their hearts: for this is the effect of the reproach, that they were unmindful of their Rock...
We have here a description of the apostasy of Israel from God, which would shortly come to pass, and to which already they had a disposition. One would have thought that a people under so many obligations to their God, in duty, gratitude, and interest, would never have turned from him; but, alas! they turned aside quickly.
Commenting on Deuteronomy 32:15-18
And when the Lord saw it,.... The disregard of the Jews to Christ, their forgetfulness of him, their disesteem and rejection of him; their continuance of sacrifices, when the great sacrifice was offered up; their setting up other messiahs and saviours, and the idol of their own righteousness, in opposition to the righteousness of Christ; all which not only as the omniscient God he saw...