See:
Galen Johnson : The Protestant Reformers’ Readings of Romans 9-11, with Modern Critical Response - Quodlibet Journal
"During the Reformation, Luther could not decide whether Paul thought all Jews would be saved, and Calvin equated “all Israel” in 11:26 with believers in Christ, both Jewish and Gentile.
[119] What insights have come from modern scholarship on the matter of Israel’s salvation?"
"Luther thought that “all Israel” was an ethnic designation, while Calvin proposed that it denotes all believers in Christ, Jew and Gentile.
[126] Barth still follows Calvin that “Israel” in 11:26 is the combination of historic Israel and the church."
See:
What does “all Israel” in Romans 11:26 mean? Does it mean that one day every single Jew will be saved? - Pilgrim Covenant - Reformed Church in SingaporeThis writer says he prefers the view "... which is held by Calvin that “all Israel” refers to all the elect, including Jews and Gentiles. The reason for this is that verse 25 is actually about the conversion of the Gentiles and the blindness of the Jews. It appears rather strange to me that verse 26 should speak abruptly about the salvation of the sum total of the elect
Jews. Would it not be more reasonable for Paul to be referring to the whole number of the elect?"
See:
What does “all Israel” in Romans 11:26 mean? Does it mean that one day every single Jew will be saved? - Pilgrim Covenant - Reformed Church in Singapore
"Dispensationalists speak of all the Jews being converted
en-mass during the 7-year tribulation period after the Church has been raptured. This view is based on a dispensational distinction between Church and Israel, which can hardly be defended without reading into the Scriptures."
Paul says in Romans 11: 17-20 that those in unbelief were broken off the olive tree, meaning those in Old Covenant Israel who rejected Christ were broken off.
We know from Romans 11: 1-5, on the remnant of Israel who accepted Christ and became the elect that those of Old Covenant Israel who rejected Christ and were broken off were the multitude.
Yet dispensationalists insist that Romans 11: 26 says all Old Covenant Israel shall be saved.
Are the multitude of Old Covenant Israel who rejected Christ in the First Century brought back to life in the future and then all saved? Or, was the multitude of the generation of Old Covenant Israel in the First Century broken off and then centuries later another generation of Old Covenant Israel will all be saved?
We should apply Isaiah 28: 9-10 - "For precept must be upon precept...line upon line; here a little, there a little" to the issue of whether Israel in "all Israel shall be saved of Romans 11: 26 is Old Covenant Israel of the Israel of God, meaning everyone who is of the elect.
Romans 2: 28-29, Romans 9: 6-8 and Galatians 3, 3, 14, 16, 26-28 are relevant scriptures dealing with the changes that took place when God remade Old Covenant Israel. Since Old Covenant Israel of the flesh, that is, those who have the flesh DNA of Abraham was changed into the spiritual seed from Abraham, first as Christ being that spiritual seed and then all those in Christ being the seed, then how is it that God would save all Old Covenant Israel in the future, the implication being because of their DNA?
Then, in addition there is the doctrine of the remnant in Romans 11: 1-5.
Paul starts in Romans 11: 1 by saying "Hath God cast away his people? God forbid. I also am an Israelite..." Then in Romans 11: 3-4 Paul gets into the remnant of Israel by quoting I Kings 19: 18. This refers to the time of Ahab and Jezebel and the apostasy they led. They were persecuting Elijah and Elijah thought he was the only one left faithful to God. But in I Kings 19: 18 God answers by saying he still has seven thousand in Israel who have not bowed the knee to Baal. This is the remnant at that time.Paul does not here review other times in the history of redemption in which a remnant replaces the multitude who have gone off into false doctrines and false practices or have otherwise become enemies of God and his remnant.
In the Flood of Noah's time God saved a very small remnant of only eight people and began over again with that eight. After the seventy years of the Babylonian captivity, groups of people of Old Covenant Israel went with Ezra, Nehemiah,
Zerubbabel, and others to Jerusalem to restore the Wall and the temple. These groups were another remnant of Israel God used to began his people Israel all over again.
The remaking of Israel into the spiritual house of I Peter 2: 5, 9 involved a greater restoration of Israel, a transformation of Israel. That which was physical Under the Old Covenant was fulfilled in that which is spiritual in Christ and in the Holy Spirit.
So what Paul is getting at in Romans 11: 1-5 is that in the remaking of Old Covenant Israel in Christ Jesus, a remnant was again used by God to begin again his people Israel. This remnant of Old Covenant Israel who accepted Christ and were born again became the first fruits of the Israel of God, or Israel reborn in Christ. As predicted by Hosea 2: 23 a people not of the bloodline of Old Covenant Israel were added to Israel. Israel had been remade, changed and transformed into a spiritual house. But it was still Israel, the group God chose for his redemption of his people, now a much larger group than those of the Old Covenant.
In order for someone who still claims to be the chosen people based on the flesh from Abraham to join this remnant of Israel as a spiritual house, he or she becomes fully born again as a Christian and gives up his or her assumed superiority and identity in Old Covenant Israel. And - those of Old Covenant Israel of the flesh come one at a time to Christ, just as do others. Galatians 3 does not support a doctrine saying that the chosen people still exist by their physical bloodline.
The remnant of Romans 11: 5 became the Israel of God of Galatians 6: 16 and the all Israel of Romans 11: 26. Where is the multitude of Old Covenant Israel who rejected Christ in the First Century and continue to reject him? They remained in unbelief in Talmudic Judaism.