But I ask, did Israel not understand? First Moses says, “I will make you jealous of those who are not a nation; with a foolish nation I will make you angry.” (ESV)
Have you ever been in a room when two lovers begin to quarrel? It is a very awkward situation. God's relationship with the people of Israel was a relationship between two lovers. Because of the waywardness of Israel it was a relationship where God was faithful to a spouse who was not. God plays the role of the jilted lover.
Imagine God having a conversation about his lover, Israel. Would you like to listen in? Paul says in this verse that Israel should have understood what the relationship with God was about. She should have realized that God wanted a faithful bride. Because she had been unfaithful God planned to make her jealous by offering his love to another.
So, what would the new nation look like that God wanted to have a relationship with? Was she pretty? Surely, Israel would want to know who God was going to offer his love to. The reality is that God would offer his love to the Gentiles. The Gentiles were the last people on Earth the Jews would have wanted for God to love. The idea of God loving Gentiles was insulting to Jews.
Paul says that the nation he is going to use to make Israel jealous will be a foolish nation. It will be Gentiles. God is looking for a people who will love him and be faithful. He chose Israel to be that nation, but they have largely rejected his loving offer. He now offers his love to all nations; the foolish. The ugly. The rejected. You. Me. People from all nations.
Do not make the mistake that Israel did. If God offers you his love, love him back! Be faithful. Do not chase after the pleasures of this world. He will be all that you could ever imagine.