John Calvin Commentary Deuteronomy 32:18

"Of the Rock that begat thee thou art unmindful, And hast forgotten God that gave thee birth." — Deuteronomy 32:18 (ASV)

Of the Rock ²⁶⁸that begat thee. He again underscores the people's guilt by referring to their ingratitude, since they did not fall through ignorance but willfully suppressed the knowledge of God that should have shone brightly in all their hearts.

For the point of this rebuke is that they were unmindful of their Rock.

This means they would never have surrendered themselves to their ungodly superstitions unless they had deliberately forgotten the God whom, by the clearest proofs, they had experienced as the foundation and support of their salvation.

²⁶⁸ Lat., “of the God,” etc.“of the God,” etc.