Romans 11:11
I say then, Have they stumbled that they should fall? God forbid: but rather through their fall salvation is come unto the Gentiles, for to provoke them to jealousy. I say then, Have they stumbled that they should fall? God forbid: but rather through their fall salvation is come unto the Gentiles, for to provoke them to jealousy.
Israel stumbled and fell, even rejecting His Son, yet that stumbling was not a fall meant to be final and beyond recovery, for God did not cast them off beyond hope and it remains possible for them to rise again. Through their fall and diminishing and casting away, salvation and reconciliation and riches have come to the Gentiles, revealing God's grace at work among the Gentiles as well as among the Israelites. That bestowal of salvation upon the Gentiles was purposed to provoke Israel to jealousy and emulation, stirring the Jews to seek that same salvation too, so that some of them might be saved.
Paul magnified his office as apostle to the Gentiles in hope that by the Gentiles' reception of salvation he might stir his own people to emulation and by all means save some of them. Blindness has happened to Israel only in part and only until the fulness of the Gentiles comes in, for their fall is the riches of the world and their diminishing the riches of the Gentiles. How much more will their fulness and receiving bring far greater riches, even as life from the dead. If they do not remain in unbelief, God is able to graft the natural branches into their own olive tree again, the true stock, which is Christ Jesus.
Gentiles therefore must not despise the Jews, nor boast against the branches, nor be high-minded, but must fear and continue in God's goodness. For among the Jews God has mighty men who will proclaim the truth and God's law with power, and many of the seed of Israel will be converted and accept Christ and the truth. The chapter outlines a work for the Jews that must not be ignored but must be carried out with special wisdom of God and righteousness, clearing the King's highway and giving the Jews every opportunity to come to the light.
A great work still remains to be done to lead many of the Jewish people to accept Christ and be grafted again, including providing a refuge and training home for Jews who accept Christ and are cut off from their people, that they may learn to work for their own people. The rejection of the Jews and the calling of the Gentiles is one of the deep things of God, a mystery that few comprehend or try to ascertain. It belongs to the deep mysteries and doctrines of the Bible that require deep thought to understand, alongside beautiful truths that all may understand, since the Bible is a progressive book and finite minds do not yet understand the Old and New Testaments as they will when God opens His Word to the understanding and communication of intelligence grows.