The "so all Israel will be saved" represents spiritual Israel, not the earthly nation of Israel. All of spiritual Israel will/must become saved.
It means that all who remain in true belief do so as a result of having been saved; those who fall-away were never of the saved - their belief superficial, temporary, not true belief and not from the heart.
[1Pe 1:4-5 KJV]
4 To an inheritance incorruptible, and undefiled, and that fadeth not away, reserved in heaven for you,
5 Who are kept by the power of God through faith unto salvation ready to be revealed in the last time.
I don't follow your point. Everyone born-again became/becomes grafted in by God because being born-again is the result of salvation - only those grafted in by God remain so. The unsaved who claim to be Christians, will eventually fall away, that at the end, all who remain were those grafted in by God.
Nope. God made no such promise to regraft in the whole earthly nation of Israel just because He removed the nation and its people as a whole. Those regrafted are those who were chosen by Him individually.
Did you read the verses I included in my prior post? They unequivocally state that it would be impossible for the earthly nation of Israel to regain any standing with God. Instead, it is the true spiritual Church alone that has become the nation and the people of God. They are spiritual Israel - it alone the bride of Christ, and Christ will not have two brides.
[Rev 21:2 KJV] 2 And I John saw the holy city, new Jerusalem, coming down from God out of heaven, prepared as a bride adorned for her husband.
Romans Chapter 11 - Israel Is Not Cast Away
Vs 1, Paul begins with a bold declaration: "Has God cast away His people? God forbid." He points to himself as proof; an Israelite, of the seed of Abraham, from the tribe of Benjamin. Israel is not rejected, disowned, or replaced.
Vs 5,6, Currently there is a remnant/a small believing minority of Israelite believers. God always preserves a faithful core.
Vs 7,8,9 Though a believing remnant sees clearly, the rest are blinded. "God has given them the spirit of slumber, eyes that they should not see & ears that they should not hear, unto this day." (See Deut. 29:4; Isa. 29:10.)
This blindness is real, but it is not final.
VS 11, Paul asks: "Have they stumbled that they should fall?" Answer: No! Their stumbling opened the door for salvation to come to the Gentiles, to provoke Israel to jealousy.
Vs 20, Unbelieving Israelite branches were broken off because they rejected Christ’s law-fulfilling, sin-atoning work. Gentiles, by faith in Jesus' finished work, have been grafted into Israel’s covenant promises. (See Eph. 2:12.)
Vs 25 Paul unveils a divine mystery: Israel's blindness that's partial & temporary. It will last "until the fulness of the Gentiles be come in." God’s plan includes both Gentile salvation & Israel’s restoration.
Vs 26, At that time, "all Israel shall be saved." As written: "There shall come out of Sion the Deliverer & shall turn away ungodliness from Jacob = Israel. Messiah Himself will complete the work.
Vs 29, "For the gifts and calling of God are without repentance." God chose Israel & will not change His mind. Done deal!
God has not rejected, disowned or replaced Israel with the NT church. The Church/believers in Jesus finished sin atoning sacrificial work. Have been grafted into God's covenants of promise. I.E. Access to our Great God & savior, Jesus the Christ!
Romans 11 isn't about replacing Israel with the Church. It's about inclusion, reconciliation & God's unchanging covenant faithfulness.
The Church/believers in Jesus' finished, sin-atoning sacrifice. Have been grafted into the covenants of promise. Israel remains chosen & Gentiles are included. Together they testify to the mercy of our great God and Savior, Jesus Christ.
Eph 2:12 That at that time ye were without Christ, being aliens from the commonwealth of Israel, and strangers from the covenants of promise, having no hope, and without God in the world:
3O the depth of the riches both of the wisdom and knowledge of God! how unsearchable are his judgments, and his ways past finding out!
34 For who hath known the mind of the Lord? or who hath been his counsellor?
35 Or who hath first given to him, and it shall be recompensed unto him again?
36 For of him, and through him, and to him, are all things: to whom be glory for ever. Amen.