And this will happen only after Christ comes as the Deliverer to Zion (Jerusalem), and removes ungodliness from Jacob (Israel).And thus, as the Bible says “ALL Israel will be saved”
Then shall the LORD go forth, and fight against those nations, as when he fought in the day of battle. And his feet shall stand in that day upon the mount of Olives, which is before Jerusalem on the east, and the mount of Olives shall cleave in the midst thereof toward the east and toward the west, and there shall be a very great valley; and half of the mountain shall remove toward the north, and half of it toward the south. (Zech 14:3,4)
Other Scriptures tell us that only one-third of all the Jews who will be gathered from all over the world to Israel will be saved.
And it shall come to pass, that in all the land, saith the LORD, two parts therein shall be cut off and die; but the third shall be left therein. And I will bring the third part through the fire, and will refine them as silver is refined, and will try them as gold is tried: they shall call on my name, and I will hear them: I will say, It is my people: and they shall say, The LORD is my God. (Zech 13:8,9)
In view of the Gospel we need to understand that what Paul was saying is that all BELIEVING Israel (from every tribe) will be saved (those who call upon the name of the LORD). All twelve tribes will be settled in greater Israel, and God knows exactly who is in which tribe. That some will not believe even after they visibly see Christ. But there will be great mourning, repentance and conversion when all Israel is saved.