Jamieson, Fausset and Brown on Romans 10:19

19. But I say, Did not Israel know?--know, from their own Scriptures, of God's intention to bring in the Gentiles?

First--that is First in the prophetic line [De Wette].

Moses saith, &c.--"I will provoke you to jealousy ('against') [them that are] not a nation, and against a nation without understanding will I anger you" (De 32:21). In this verse God warns His ancient people that because they had (that is, in aftertimes would) moved Him to jealousy with their "no-gods," and provoked Him to anger with their vanities, He in requital would move them to jealousy by receiving into His favor a "no-people," and provoke them to anger by adopting a nation void of understanding.