Deuteronomy 32:21 - Joseph Benson’s Commentary on the Old and New Testaments

They have provoked me to anger with their vanities By vanities here are meant the fictitious deities of the nations with whose worship the Israelites corrupted themselves: see Jeremiah 8:19; Jeremiah 14:22. I will move them to jealousy, &c. God here threatens to repay their frequent revolts from him in their own kind, in a way most mortifying to their proud spirits; by causing the very Gentile nations, whom they much despised, not only to become their masters and conquerors, but also to be taken into his covenant, while they themselves were excluded from it. See Matthew 21:43-44; Romans 10:19. With those that are not a people With the heathen nations, who were none of God's people, who scarce deserved the flame of a people, as being without the knowledge and fear of God, which is the foundation of all true policy and government, and many of them destitute of all government, laws, and order. And yet these people God declares he will take in their stead, receive them, and reject the Israelites, which when it came to pass, how desperately did it provoke the Jews to jealousy! A foolish nation So the Gentiles were, both in the opinion of the Jews, and in truth and in reality, notwithstanding all their pretences to wisdom, there being nothing more foolish or brutish than the worship of idols.