(Rom 11:11) Again I ask: Did they stumble so as to fall beyond recovery? Not at all! Rather, because of their transgression, salvation has come to the Gentiles to make Israel envious.
Paul makes two points. His second is that God brought salvation to the Gentiles to provoke the Jews to jealousy. He made that point earlier. It comes straight from Deu 32.
His first point is that the Jews can recover from this unspeakable disaster! Their fate is not hopeless. (All they have to do is believe in Jesus!)
(Rom 11:12) But if their transgression means riches for the world, and their loss means riches for the Gentiles, how much greater riches will their fullness bring!
Notice that Paul says the Jews (as a nation, not individuals) are lost because of their “transgressions.” And his point is that if it pleases God to bring in the Gentile, God will surely be more pleased to bring in both the Jews and Gentiles — which is plainly true.
(Rom 11:13-15) I am talking to you Gentiles. Inasmuch as I am the apostle to the Gentiles, I make much of my ministry 14 in the hope that I may somehow arouse my own people to envy and save some of them. 15 For if their rejection is the reconciliation of the world, what will their acceptance be but life from the dead?
Paul now combines the themes of chapters 10 and 11. “How beautiful are the feet” of Paul as apostle to the Gentiles! But in a marvelous irony, his work among the Gentiles should redound to the benefit of the Jews by provoking them to jealousy and faith in Jesus!
Now, if the solution is for God to elect them so they’ll receive prevenient grace and so have faith and be saved — what’s the point of Paul seeking to arouse them to jealousy? Indeed, why would God say that he intends to deal with their faithlessness by provoking them to jealousy? Jealousy is a freewill emotion — and quite unnecessary in the Calvinist scheme.