John Calvin on Deuteronomy 32:18

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: as much as to say, that they would never have given themselves up to their impious superstitions, unless they had cast into voluntary oblivion that God whom, by the most conspicuous proofs, they had experimentally found to be the foundation and support of their salvation.