The following is a prophecy concerning "Spiritual Israel" and the only members of that Israel will be the physical descendants of Abraham, Isaac and Jacob:
"Behold, the days come, saith the LORD, that I will make a new covenant with the house of Israel, and with the house of Judah: Not according to the covenant that I made with their fathers in the day that I took them by the hand to bring them out of the land of Egypt; which my covenant they brake, although I was an husband unto them, saith the LORD: But this shall be the covenant that I will make with the house of Israel; After those days, saith the LORD, I will put my law in their inward parts, and write it in their hearts; and will be their God, and they shall be my people. And they shall teach no more every man his neighbour, and every man his brother, saying, Know the LORD: for they shall all know me, from the least of them unto the greatest of them, saith the LORD: for I will forgive their iniquity, and I will remember their sin no more" (Jer.31:31-34).
In this passage we can see that the "fathers" of those who will be in both the house of Israel and the house of Judah are the physical descendants of Abraham, Isaac and Jacob. Their "fathers" broke the LORD's covenant and it was the physical descendants of Jacob who did that. Therefore, since their fathers are the physical descendants of Jacob then those of both the house of Israel and the house of Judah will also be the same physical descendants.
So these verses prove that sometime in the FUTURE all of the physical descendants of Abraham, Isaac and Jacob who will belong to both houses will be saved.