Let us establish first this principle I am sure we can all agree on…..
"For there is no difference between the Jew and the Greek: for the same Lord over all is rich unto all that call upon him." Romans 10:12
Principle = God will respond richly to all who call on Him, whether Jew or Gentile.
To consider what Romans 11:26 - "And so all Israel shall be saved” means we need to work through Romans 11 to see what Paul meant by ‘Israel’ here and what he meant by ‘All Israel’.
However let us start in Romans 10:21, as we know this is one letter and there were no chapter divisions originally and this defines who Paul is talking about at this point.
"But to Israel he saith, All day long I have stretched forth my hands unto a disobedient and gainsaying people.”
So Israel here we would agree is Israel the nation (or ethnic Israel), as it cannot be a synonym for the church, seeing they are a disobedient people. I am going to use the term ‘ethnic Israel’ to distinguish from ‘spiritual Israel’.
Next verse is Romans 11:1 "I say then, Hath God cast away his people? God forbid. For I also am an Israelite, of the seed of Abraham, of the tribe of Benjamin.”
So has God cast away his people? Which people? This must be ethnic Israel based on context and Paul defines that he is one of them by natural lineage. GOD HAS NOT CAST THEM AWAY, because Paul is proof, being one of them.
Romans 11:2-5: "God hath not cast away his people which he foreknew. Wot ye not what the scripture saith of Elias? how he maketh intercession to God against Israel, saying,”
"Lord, they have killed thy prophets, and digged down thine altars; and I am left alone, and they seek my life.”
"But what saith the answer of God unto him? I have reserved to myself seven thousand men, who have not bowed the knee to the image of Baal.”
"Even so then at this present time also there is a remnant according to the election of grace.”
So Paul makes the point here that although it may appear that ethnic Israel has completely rejected the LORD (like in the days of Elijah), in actual fact there is a remnant that God has within ‘ethnic Israel’ who remain faithful. This remnant would include the Jewish apostles, the Jew Paul and all the early Church that was by majority Jewish at the beginning. This remnant are these elected (chosen) by grace.
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.”
Who is Paul talking about as having stumbled? It is not gentiles, it is not the faithful remnant of Israelites, but the rest, the majority of his people Israel. However Paul says they have not stumbled to the point of a fall (God forbid). This is where the KJV confuses the issue, because he seems to contradict himself by saying, "but through their ‘fall’ salvation has come to the gentiles”. The second word 'fall' here is different and is better translated ‘ sin’. When he says "that they should not fall” the word fall is to fall away completely.
Romans 11:12: "Now if the fall (sin) of them be the riches of the world, and the diminishing of them the riches of the Gentiles; how much more their fulness?”
Now in vs. 17-21 Paul use the analogy of the olive tree.
"And if some of the branches be broken off, and thou, being a wild olive tree, wert graffed in among them, and with them partakest of the root and fatness of the olive tree;"
"Boast not against the branches. But if thou boast, thou bearest not the root, but the root thee.”
"Thou wilt say then, The branches were broken off, that I might be graffed in."
"Well; because of unbelief they were broken off, and thou standest by faith. Be not highminded, but fear:"
"For if God spared not the natural branches, take heed lest he also spare not thee.”
So we note here Paul is talking about a ‘natural’ olive tree with ‘natural’ branches as an analogy for natural (ethnic) Israel and natural (ethnic) Isralites (or Jews) compared to a ‘wild’ olive tree and branches(gentiles).
Romans 11:24-25 "For if thou (gentiles) wert cut out of the olive tree which is wild by nature, and wert graffed contrary to nature into a good olive tree: how much more shall these (ethnic Israel), which be the natural branches, be graffed into their own olive tree?”
"For I would not, brethren, that ye should be ignorant of this mystery, lest ye should be wise in your own conceits; that blindness in part is happened to Israel, until the fulness of the Gentiles be come in.”
We are told not to be ignorant about the fact that this blindness to Israel is only in part, UNTIL the fulness of the gentiles comes in. This can only mean that there is a time (in God’s pre-determined plan) when all those who are gentile by nature have come into the church (the body of Christ). Note: fullness of the gentiles is completely different to ‘the times of the gentiles’. Fullness of the gentiles is to do with believers in this context. 'Times of the gentiles' is spoken of the unbelieving nations that dominate the people of Israel.
ROMANS 11:26 Now we are here! So we have seen the context and consider what this means.
"And so all Israel shall be saved: as it is written, There shall come out of Sion the Deliverer, and shall turn away ungodliness from Jacob:”
First we have seen that ‘Israel’ all the way through this chapter has always meant ‘ethnic Israel’, therefore it would be without warrant to change this meaning half way through a sentence.
Let’s also clarify the words ‘and so’ in this verse. It is the greek word ‘houtÅ’ and means ‘in this way’. So ‘in this way’ (after the fullness of the gentiles has come in) Israel will no longer be blinded and be grafted back in. Because "the deliverer shall turn ungodliness from Jacob”. Notice it says ‘Jacob’ This reinforces the fact Paul is clearly talking about his brothers after the flesh (ethnic Israel).
All Israel in the context of all we have looked at in this chapter, must mean all those within natural (ethnic) Israel who will be the true (spiritual)Israel through faith and obedience to Christ. In the same way there will be a fullness of the gentiles within the church, there will also be a fullness of Israel (the 'all') who make up the church and we will be one church (Jew and gentile). We have not reached this point of the fullness of gentiles yet and ungodliness being taken away from Jacob, but the re-gathering of Israel into the land is part of that process. We see an increasing number of Jewish churches and fellowships in the land of Israel . it is estimated that today there are over 20,000 Jewish believers and over 150 messianic congregations in the land of Israel, compared to less than a handful in the 1970s. Are we seeing the beginning of this blindness being taken away?
Romans 11:28-29 "As concerning the gospel, they are enemies for your sakes: but as touching the election, they are beloved for the fathers' sakes. For the gifts and calling of God are without repentance.”
In the context of all Paul has told us about Israel, he says the gifts and calling of God are without repentance. God has not and will not change His mind in regard to Israel.