Romans 10:19

But I say, Did Israel not know? First Moses saith, I will provoke you to jealousy with that which is no nation, With a nation void of understanding will I anger you.

Just as Romans 10:18 was concerned with whether or not Israel heard, this one addresses itself to the question of whether or not they knew. The answer in both cases is affirmative. The particular truth Paul here credited them with knowing was that God would call the Gentiles into his favor, at last producing jealousy and anger on Israel's part. Thus, not merely the fact of extending God's favor to the Gentiles is in view, but also the anger and jealousy of Israel that would result from it. Paul's quotation of Moses in this place (Deuteronomy 32:21) was the equivalent of appealing to the supreme court of Jewish authority, for the Jews respected no authority as higher than that of the great lawgiver.

Paul's method in this place, as so frequently throughout the epistle, is that of the diatribe, in which theoretical questions are raised, as if from a hearer, and then refuted. The objection dealt with here might be stated thus, "Well, perhaps Israel did not know that the Gentiles were to be called." But, of course, they did know. Beginning with the great promise of Abraham that in him "all the families of the earth" should be blessed, and coming right on down to the words here spoken by Moses, as well as the warnings of all the prophets, the scriptures bore ample testimony to the calling of the Gentiles. God had repeatedly apprised Israel of what he would do.