Romans 11:23-29
[23] And even they (unbelieving Jews), if they do not continue in their unbelief, will be grafted in (to the tree; ‘True Israel/Chruch), for God has the power to graft them in again. [24] For if you (Gentiles) were cut from what is by nature a wild olive tree, and grafted, contrary to nature, into a cultivated olive tree, how much more will these, the natural branches, be grafted back into their own olive tree.
[25] Lest you be wise in your own sight, I do not want you to be unaware of this mystery, brothers: a partial hardening has come upon Israel, until the fullness of the Gentiles has come in. [26] And in this way all Israel will be saved, as it is written,
“The Deliverer will come from Zion,
he will banish ungodliness from Jacob”;
[27] “and this will be my covenant with them
when I take away their sins.”
[28] As regards the gospel, they are enemies for your sake. But as regards election, they are beloved for the sake of their forefathers. [29] For the gifts and the calling of God are irrevocable.
Now: granted there are arguments over what the meaning of “all Israel” means. Some claim it means the totality of ‘elect Jews’ down through history. This is possible. However, I’m less certain of that. The passage, if read from the beginning of Chapter 11, seems to highlight 3 different people groups. Paul is speaking TO saved Gentiles about their inclusion onto the ‘tree’. He is speaking about how the ‘elect of Israel’ were not abandoned in God’s promises…indeed, he is an example of those who remained on the natural tree. But he is also clearly speaking about ‘Israel’ in terms of those who have been ‘broken off’ from the tree. That is; Jews who do not believe in Messiah and are therefore “enemies in regards of the gospel”.
We know that in light of the New Covenant no one will be saved unless they come to Christ…unless they are ‘on the tree’…be they natural branches or grafted on branches. To my mind, the most natural reading of this passage, in light of the 3 people groups Paul is highlighting, is that when “the fullness of the Gentiles has come in”, the “partial hardening” of Israel (the broken off branches” will be lifted. Thus, God’s “calling and promises to the forefathers” will be fulfilled, as they are irrevocable.
Will this mean all Jews who remain alive at that time? I don’t know. But I suspect a large portion of them. I think, as we see at the end of Matthew 23, that they will cry out “Blessed is he who comes in the name of the Lord”…finally realising who their Messiah is.