Romans 10:19 But I say, did Israel not understand? First Moses says, “I will provoke you to jealousy by those who are not a nation, with a nation empty of understanding I will vex you.”
So what if “Israel did not understand;” does that make God a liar? Romans 3:3-4a So what if some did not trust? Will their lack of faith nullify God’s faithfulness? May it never be! Let God be true even if every man is a liar. God is not a liar, man is.
But Paul is asking a question, “Did Israel not understand?” His point is (and the reason he’s asking the question is) that Israel did understand, being provoked to jealousy by a people who were not a people. Paul is quoting from … Deuteronomy 32:21 They made Me jealous with a non-god. They vexed Me with airy idols. So I will make them jealous with a non-people. With a foolish nation I will vex them. … Read on here