Read Romans 11.
This chapter is pivotal in connecting the promises God made in the Old Testament to the future of the nation of Israel. In the two previous chapters, the Apostle Paul addressed the national rejection of Jesus by the Jews and the consequences. Now, in chapter eleven, he brings clarity to any confusion or doubts about Israel's future.
1. Israel Rejected. (vv.1-10)
The question is "Has God rejected the Jews?" Are the promises, therefore, nullified that He made to Abraham in Genesis 12, 15 and 17? The Bible's answer could not be more plain, "By no means!" Though nationally Israel does not worship Jesus at this time, it is not a total rejection, because individual Jews were and are being saved through faith in Christ. Paul called it "a remnant" and offered himself as an example. As for the nation, Israel "stumbled" but the fall is not fatal.
2. Gentiles Grafted. (vv.11-24)
Israel is depicted as an Olive tree. In the sovereign plan of God, during this time in world history, some of the original branches have been broken off in order to graft in some "wild" branches (Gentiles). The purpose is consistent with the Lord's promise to Abraham and the Great Commission. Persecution of Christians in Jerusalem became a key means for the Good News of Jesus to spread from Israel for "the reconciliation of the world". Seeing God work in other nations is designed to make Israel "jealous."
3. Israel Restored. (vv.25-32).
The rejection by the Jews is "a partial" hardening of their national hearts and it is temporary. Notice the phrase "until the fullness of the Gentiles has come in". Jesus used the same term in discussing the Tribulation Period in Luke 21:24. This awful time will be used to prepare Israel for the appearance of the Messiah and the establishment of His kingdom "on the throne of his father David" in Jerusalem. "And in this way all Israel will be saved." (v.25) All the prophecies concerning the earthly kingdom and Israel's prominence will be fulfilled in that future restoration. It will be the ultimate fulfillment of Jeremiah 31 regarding the New Covenant.
4. God Glorified. (vv.33-36)
Under the inspiration of the Holy Spirit, Paul became so excited and in awe of the purposes and plans of God that he broke out in praise. The truths in this chapter are not merely great theological content, but they demonstrate how far beyond God's thinking is than ours. Indeed, He is in control. He is all sufficient and self-sufficient. No one can fully comprehend His works. No one is God's counselor. God is no one's debtor. All things come from Him in order to glorify Him. Soli Deo gloria!