How can you believe that ALL Israel will be saved? You don't and you can't.
Of course you think that you know more than Paul because he certainly believed that all Israel shall be saved:
"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: For this is my covenant unto them, when I shall take away their sins" (Ro.11:26-27).
You believe that 2/3 of the Jews will be slaughtered - and the 1/3 that remain will be saved. That isn't all Israel! That's what's left of Israel. You believe that a remnant of Israel will be saved. I do to.
Again, you deny what Paul said as well as what is written here:
"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).
There has never been a time when all of the physical descendants of Abraham, Isaac and Jacob plus all of the Gentile converts to Judaism had their sins forgiven.
You live in a fairy tale world if you think that happened sometime in the past. It has never happened and the preterists have no place for its fulfllment in the future.
So according to your idea the LORD makes promises and then refuses to honor those promises.
The message is clear that certain literal physical sons of Abraham will not be counted as true sons - yet certain non-related people will be counted as true sons.
No one argued that is all circumstances that all of the physical descendants of Abraham will be counted as true sons. On the other hand, it is a fact that some of the physical descendants are counted as true sons.
It is also a fact that those who will receive the promise of the New Covenant at Jeremiah 31:31-34 are either the physical descendants of Abraham, Isaac and Jacob or Gentile converts to Judaism who have been circumcised. There has never been a time when every single one of those people have had their sins forgiven.
Apply this clear teaching to the Jeremiah prophecy and you will see how ALL of Abraham's true children have had all their sins forgiven.
The fathers of those who will receive the promises under the New Covenant are described this way:
"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" (Jer.31:32).
Not only are the "fathers" of those who will receive the blessings of the New Covenant the physical descendants of Abraham, Isaac and Jacob but it is clear by their actions that they couldn't be described as a so-called "spiritual Israel":
"They have turned aside quickly out of the way which I commanded them: they have made them a molten calf, and have worshipped it, and have sacrificed thereunto, and said, These be thy gods, O Israel, which have brought thee up out of the land of Egypt" (Ex.32:8).
With these facts in view it is evident that their fathers were the physical descendants of Abraham, Isaac and Jacob and not members of the so-called spiritual Israel.
You say the following:
Apply this clear teaching to the Jeremiah prophecy and you will see how ALL of Abraham's true children have had all their sins forgiven.'
Yes, at Jeremiah 31:34 we can see that all of the physical descendants of Abraham, Isaac and Jacob are Abraham's true children because they have all had their sins forgiven.
And there has never been a time when all of the physical descendants of Abraham, Isaac and Jacob plus all the Gentiles converts to Judaism have had their sins forgiven. So the promises of Jeremiah 31:31-34 have not been fulfilled. And since you have no place for the fulfillment of these promises in your eschatology then that means that you worship a God who makes promises and then refuses to honor those promises.