So God’s plan, Paul says, is that Israel currently reject Jesus as Messiah, which in some way must have facilitated the Gentile mission in Paul’s mind. Paul also saw the acceptance of the gospel by Gentiles as somehow making his own people jealous. He does not spell out exactly what he meant, but he apparently believed it would somehow eventually lead ethnic Israel back to God, to belief in Jesus as Messiah.
His argument thus reaches its climax in 11:25-32. Part of Israel is currently experiencing a hardening (11:25). There is no question what Israel Paul has in mind here. He is talking about the “hardened” part, those ethnic Jews who have not believed in Jesus. He is talking about the “natural branches” that God has grafted out, unbelieving Jews. The purpose, as he has said, is so that the “full number” of the Gentiles can come in.
But then, Paul says, “all Israel will be saved.” Again, Paul’s statement may be difficult for us to process, but it is not ambiguous. It is the contrast between “part” and “whole.” Right now part is hardened. Then all will be saved. Some have ripped this statement out of its literary context as if to say by “all Israel will be saved” Paul is simply saying that all true Israel will be saved, hearkening back to 9:6. But not only would such a meaning be pointless to say—“all the saved will be saved.” It ignores the clear train of thought. Right now part is out. Then all will be in.
Christ will thus take away the current sins of Israel (11:27). He will “turn godlessness away from Jacob” (11:26). Paul is not very clear about what he is saying. He says that “The deliverer will come from Zion,” referring to Jesus. But is he talking about Jesus coming out of Zion in the future or about Jesus previous coming out of Zion?  Is Paul saying Israel will believe around the time of Jesus’ return from heaven, perhaps in preparation for Christ’s return or as a consequence of his return? Or is he simply quoting a passage that generally indicates the Jews will believe in their messiah?
Either way, Paul is clearly pointing to the eventual salvation of Israel. Right now, they are God’s enemies because of what he is doing with the Gentiles (11:28). But they are still the elect of God, the chosen ones. “God’s gifts and his call is irrevocable” (11:29), meaning that God will never turn his back on Israel. He might destroy a generation, but he will not break his word to Abraham. The Gentiles have received mercy because of Israel’s disobedience (11:30). But eventually Israel will also receive mercy because of what God is doing with the Gentiles (11:31), and God will then have mercy on everyone (11:32).
So it is not too difficult to understand what Paul was saying in these verses. What is difficult is for us to know what to do with them today! No doubt a certain kind of Christian expectation about the destiny of Israel played a role in the reestablishment of Israel as a nation in 1948. Is this political restoration what Paul was predicting?
 Interestingly, Paul seems to have modified the Old Testament quotation slightly, something New Testament authors regularly felt free to do. The Greek Paul was reading said, “The redeemer will come because of Zion.” Paul—or the tradition he was using—changed it to “The redeemer will come out of Zion.”