What did Moses prophesy about the Gentiles coming to God?
According to Paul, Moses foretold that another nation—the Gentiles—would come into fellowship with Israel's God, and that Israel would hate them for it. This is exactly what happened when Paul preached salvation to the Gentiles, as the Jewish people fought the Gospel.
Les explains that Paul, in verse 21, recounts how Jesus sent him far hence to the Gentiles. When Paul mentioned the word 'Gentile,' the crowd lifted their voices and said, 'Away with such a fellow from the earth, for it is not fit that he should live.' Paul then declares that Moses foretold this very response: another nation would come into fellowship with Israel's God, and Israel would hate them for it. Les points out that the more the Gentiles succumbed to the Gospel, the more the Jewish people fought it, except for a few. He notes this is no different today, citing Israel's Law of Return, which tries to keep out Christians or even Jewish people who are professed believers in Christ, because religiously they are still hidebound, thinking there is no room for a Gentile in their so-called religion.
They have moved me to jealousy with that which is not God; they have provoked me to anger with their vanities: and I will move them to jealousy with those which are not a people; I will provoke them to anger with a foolish nation.
But I say, Did not Israel know? First Moses saith, I will provoke you to jealousy by them that are no people, and by a foolish nation I will anger you.