I would suggest that only Israel is saved. Then it's easy to understand why, and how, all Israel is saved.
I don’t necessarily disagree. But people tend to get upset when you try and align the Church and Israel, so I find it helps to try and step by step breakdown that, in point of fact, there is only ‘in Christ’…which is being grafted onto the tree. Which yes, is “Israel” in truth…but is also the Church.
I think people sometimes forget that the Church started as a purely Jewish thing. The Church was borne of the 12 essentially, and the other close disciples of Christ. It moved to the 5000 on Pentecost, ’devout’ Jews in Jerusalem, but from other nations, which helped spread it. In that way, its almost impossible to separate the Church from believing Jews. Because believing Jews have always been the elect body of God, stretching back to Abraham.
I think what we see in Romans 11 is what we see playing out in history, really. In the OT we saw national Israel being the people group that God chose his ‘elect’ from primarily…with a few Gentiles tossed in there…Rahab, Ruth, for example. But when Christ ‘opened salvation up’ to the nations, and we saw the Jews reject their Messiah, we saw a swing…masses of Gentiles coming to faith…with a few Jewish brothers and sisters among the believers. But I think Paul points to a time when the floodgates will open. The pendulum will swing again and the people who were first elected to bring hope to all the Nations will, in large numbers, be bought to see that Jesus Christ is their Messiah. It may be this will be in conjunction with Gentile believers coming in as well. But…as Paul elsewhere refers to ‘the time of the Gentiles being fulfilled’, and also to a time where the Church as we know it having a massive apostasy…It may very well be that a time will come when the Gentiles being grafted onto the tree…onto ‘true Israel’ if you prefer, will cease, and large numbers of ethnic Jews will begin to be grafted back onto it.
I really don’t know what it will look like, but it does seem to me that Paul does speak of a future in gathering of ethnic Jews. And I think that is wonderful. Because I look at so many of them today, clinging to faith in YHWY…and he IS the true God! But without acknowledging his Son Jesus….they are, in fact, rejecting truth, and God himself. And that is tragic. It is glorious when an ethnic Jew comes to know their Messiah, so I pray God will work a miracle there.