The Consequences of Israel's Unbelief
Paul tells us that God's underlying purpose in blinding the eyes of the majority of the Israelites was to cause the Old Covenant to fail, so that a greater Covenant could be established. If the Israelites had not broken the Old Covenant, then salvation would have come by means of their vow in Exodus 19:8 and by their ability to fulfill that vow. Yet John 1:11-13 says,
11 He came to His own [tribe], and those who were His own did not receive Him. 12 But as many as received Him, to them He gave the right to become children of God, even to those who believe in His name, 13 who were born [begotten] not of blood[line], nor of the will of the flesh, nor of the will of man, but of God.
Men could be saved neither by their genealogy nor by their own strength of will. Having proven this fact over a period of 1480 years from Moses to Christ, He then established the New Covenant, which was truly unconditional, based upon God's ability to turn the hearts of all men to Himself.
As a result of the cross, He began to regather ALL of the "not-My-people" into His Kingdom through faith in Jesus Christ alone. The remnant of grace would come first, followed later by the rest of the Israelites and the world in general, when every knee bows and every tongue confesses Him as Lord to the glory of God. For the vast bulk of humanity, the Great White Throne will be the day that their eyes are opened to see God for who He really is.
One Law for All Men
God's purpose in blinding Israel was to make them "not My people," so that all of the ethnos, having the same legal status, could be brought into the New Covenant on an equal footing. Bound up in all of this is the principle of jealousy, for Israel's loss of "My people" status was designed to make them jealous of God's favorable treatment of the other nations.
The downside of this jealousy is that as long as either Jews or Israelites remain blind, they continue to seek ways to present themselves as better—or more worthy—of God's favor than other ethnos. So far, this has been their most prominent defense against the divine judgment. They still want to maintain a genealogical basis for their claim to covenant status. They become jealous when they hear of the "equal citizenship" of all who are in Christ.
But in the end, when their eyes are opened to the Truth, they will have to acknowledge that their pedigree is inadequate as proof of citizenship. Israel's pedigree only proves them to be the descendants of idolaters and unbelievers who broke their covenant with God and who were cast out to become "not My people."
When they see that they are cast out while many others from the east and west are gathered to Him and blessed (Matt. 8:11, 12), then the principle of jealousy will be truly effective in causing them to repent. But they must repent on God's terms, agreeing to treat all men as equal citizens of the Kingdom. As the law says in Num. 15:15, 16,
15 As for the assembly, there shall be one statute for you [Israelites] and for the alien who sojourns with you, a perpetual statute throughout your generations; as you are, so shall the alien be before the Lord. 16 There is to be one law and one ordinance for you and for the alien who sojourns with you.
The law defines the mind and will of God. The law established equality of citizenship to all who had faith in God. The majority of the Israelites probably disagreed with this, thinking that they were exclusively chosen by virtue of their descent from Abraham. Even today many are taught that the law was exclusively for Israel only, and that it was not relevant to other people. But in spite of these misunderstandings, the word still stands: "There is to be one law and one ordinance for you and for the alien."
Not recognizing this is part of the blindness that has been placed upon the people. Only when that blindness is removed can the Kingdom of God function as it ought.
The Reconciliation of the World
Paul continues in Romans 11:12,
12 Now if their transgression be riches for the world and their failure be riches for the ethnos, how much more will their fulfillment be!
Some have understood this to mean that if the fall of the Jewish nation benefited the ethnos, then when the Jews finally accept Christ, how much more will the Jews be blessed. Such a view still retains the old idea that Jews are more chosen than others. Others have searched for the lost tribes of Israel in order to apply the same mind-set to them instead of the Jews. But this violates everything that Paul was trying to teach.
Under the Old Covenant, God's Kingdom of Israel was largely localized and centered around the Ark of the Covenant in one small spot in the world. So God blinded their eyes and hardened their hearts in order to make them fail. The Law then condemned the nation, and God divorced them, cast them out into the world of nations and scattered them throughout the world.
After Christ came to do His first work, He sent apostles to these dispersed ex-Israelites to tell them of the Messiah's work of grace. Many others had opportunity to hear the gospel as well, and so all the ethnos who believed the Gospel began to be regathered as Isaiah 56:8 had prophesied. It was not God's intent for the lost sheep to be lost forever, nor was it His intent that any man should perish. His intent was to expand the scope of the Kingdom until, as Daniel 2:35 says, it fills the entire earth.
13 But I am speaking to you who are the ethnos. Inasmuch then as I am an apostle of the ethnos, I magnify my ministry, 14 if somehow I might move to jealousy my fellow countrymen and save some of them.
These ethnos were those classed as "not My people," both of the dispersed Israelites and the other nations among whom they lived. These dispersed Israelites had already been humbled by the great divorce from God (Jer. 3:8). Having lost everything, they were far more ready to place their faith in Jesus Christ and come under the New Covenant than Paul's fellow countrymen of Judea, who still believed that the Old Covenant was in effect and saw no need for a New Covenant.
15 For if their rejection be the reconciliation of the world, what will their acceptance be but life from the dead?
It is not clear if Paul was thinking of the Judeans specifically or if he was identifying the Israelites as his "countrymen." It does not matter, of course, because both Israel and Judah had rejected Christ in their own way. It was necessary for both Israel and Judah to violate the Old Covenant in order to make room for the New Covenant, by which God might reconcile the world.
Paul believed that in the end all of the Israelites and Judahites would accept Jesus as the Christ and Heir of all things. Paul did not believe that Israel had been cast off forever. He believed the prophecies that Israel would be regathered and that God would seek out His "lost sheep" as prophesied in Ezekiel 34:11,
11 For thus says the Lord God, "Behold, I Myself will search for My sheep and seek them out."
God says further to the House of Israel in Ezekiel 36:25-27,
25 Then I will sprinkle clean water on you, and you will be clean; I will cleanse you from all your filthiness and from all your idols. 26 Moreover, I will give you a new heart and put a new spirit within you; and I will remove the heart of stone from your flesh and give you a heart of flesh. 27 And I will put My Spirit within you and cause you to walk in My statutes, and you will be careful to observe My ordinances.
Finally, He tells them in Ezekiel 37:22,
22 and I will make them one nation in the land, on the mountains of Israel; and one king will be king for all of them; and they will no longer be two nations, and they will no longer be divided into two kingdoms.
In repairing the breach between Israel and Judah, God also intends to repair the breach between Israel and the ethnos. Hence, the divine plan called for hardening the hearts of both Israel and Judah, so that they would be cast out. In their regathering, others would be gathered with them (Is. 56:8), and all would have at least one thing in common—they would share a common faith in Jesus Christ the King.
This is the resurrection of the House of Israel and of the Kingdom of God itself, as prophesied in the valley of dry bones, for we read in Ezekiel 37:13,
13 Then you will know that I am the Lord, when I have opened your graves and caused you to come up out of your graves, My people.
This is Israel's "life from the dead" that Paul mentioned in Romans 11:15.
The salvation of the ethnos did not replace the salvation of Israel (as if Israel would be lost forever, while the world would be assured of salvation). Rather, the divine plan was to save Israel while revealing the door of salvation to the whole world.
The Law of First-fruits
The salvation of the world begins with the salvation of the remnant of grace, even as the harvest always begins with the first fruits offering.
16 And if the first piece of dough be holy, the lump is also; and if the root be holy, the branches are too.
This is the law of first fruits. When the priest waved the first fruits of the barley shortly after the feast of Passover, it sanctified the entire harvest. The people could then go home and harvest their barley. No one could harvest or eat of the new crop until the first fruits offering had been made. Lev. 23:14 says,
14 Until this same day, until you have brought in the offering of your God, you shall eat neither bread nor roasted grain nor new growth.
The single sheaf of barley was like a random sampling. It represented the rest of the harvest yet in the field. When offered, it was sanctified, or set apart for divine service, and it made the entire harvest holy, opening the door to the greater harvest.
Paul brought up this law to show that the remnant of grace was the first fruit offering that would sanctify the "field" (world) for harvest. More specifically, those who inherit life in the first resurrection will be the first-fruits of a great harvest. The first resurrection is prophesied to occur at the start of the thousand-year reign of Christ (Rev. 20:4-6). After that time, the greatest harvest ever seen will begin, as whole nations will seek enlightenment found in the law of God (Isaiah 2:2-4).
The manifested sons of God will prove to the world that the biblical path is the correct one. Many will then desire to follow that same path in order to become a manifested son of God, clothed in immortality.