John Calvin Commentary Deuteronomy 32:12

"Jehovah alone did lead him, And there was no foreign god with him." — Deuteronomy 32:12 (ASV)

So the Lord alone led him. This is spoken by anticipation, in order to take away every pretext from the Israelites, should they seek, according to their custom, to mingle their superstitions with the pure service of God.

For, when they were bringing in gods of various nations from all directions, this was the excuse they commonly made: that God was not in this way deprived of His due honor. Consequently, they permitted themselves to heap together a multitude of false gods, whom they worshipped as their patrons.

But Moses anticipates them and declares that God, as He had no need of external aid, had not associated with Himself any strange gods in His preservation of the people. It therefore follows that whatever gods the people introduced, they transferred to them the honor due to the one true God.

Let us then learn from this passage that, unless God is served without a rival, religion is completely perverted by the impious mixture.