As we move later into Romans chapter 11, we find the theme for this passage.

For this is My covenant with them, When I take away their sins. Concerning the gospel they are enemies for your sake, but concerning the election they are beloved for the sake of the fathers. For the gifts and the calling of God are irrevocable. (Romans 11:27-29 NKJV)

The rejection of Israel is temporary, not because of effort or merit. The eventual re-grafting of Israel is based completely on the nature of God. While humans may change their minds or dissolve a contract, God is perfect and His word is unalterable. Once God makes an unconditional promise, He will never renege on it. To do so would mean His promise was less than perfect. And God made these covenant promises with full knowledge of what would happen in the future. God has no “Plan B” and He will never need one.

In the previous verses, Paul reiterates the temporary nature of Israel’s blindness.

For I do not desire, brethren, that you should be ignorant of this mystery, lest you should be wise in your own opinion, that blindness in part has happened to Israel until the fullness of the Gentiles has come in. And so all Israel will be saved, as it is written: The Deliverer will come out of Zion, And He will turn away ungodliness from Jacob; (Romans 11:25, 26 NKJV)

Who is the group being referred to as “all Israel” here? It is made up of the true children of Abraham. Those who have faith, whether born as Gentiles or Jews. And there will come a day when the last of the Gentiles who God foreknows will obey the Gospel is saved, and the blindness is taken away, and masses of Jews turn to the Messiah and are grafted back into the olive tree.

For as you were once disobedient to God, yet have now obtained mercy through their disobedience, even so these also have now been disobedient, that through the mercy shown you they also may obtain mercy. For God has committed them all to disobedience, that He might have mercy on all. (Romans 11:30-32 NKJV)

Just as we, as Gentiles, we’re once lost and walking in disobedience, and received mercy for salvation, God will cause Israel to turn from their disobedience because of His mercy. Thus, God will have saved both groups for one reason alone. Because He decided to do it!
Paul makes it clear that we are not qualified to determine the reasons God does things. It’s not about us, or what we think should happen. God’s ways are beyond our ability to fully fathom.

Oh, the depth of the riches both of the wisdom and knowledge of God! How unsearchable are His judgments and His ways past finding out! For who has known the mind of the Lord? Or who has become His counselor? Or who has first given to Him And it shall be repaid to him? For of Him and through Him and to Him are all things, to whom be glory forever. Amen. (Romans 11:33-36 NKJV)

It’s not about us. It’s about the glory of God. Period! And so both groups, Jew and Gentile alike, will fulfill the plan of God together. We can’t do it without them, and they can’t complete it without us. I will finish this one with what the Hebrew writer said:

And these all were commended for their faith, yet they did not receive what was promised. For God had provided something better for us, so that they would be made perfect together with us. (Hebrews 11:39, 40 NET)