Disclaimer
I believe that all of physical bloodline Israel will be saved.
I however do not agree with the OP’s interpretation that all of Israel means every Israelite.
While all of Israel can be interpreted at the individual level to mean every Israelite, it can also be interpreted in a broader sense, all twelve tribes of Israel and the statement “all of Israel will be saved” will still hold true, which would therefore mean physical bloodlines.
I therefore believe that Apostle Paul was not referring to all of Israel at the individual level but at the twelve bloodline tribe level.
So the hermeneutics revolves around the word Israel and how it was intended and used by Apostle Paul.
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Not sure where to start with this subject whether right at the very beginning before Abraham was even chosen to become a great nation Deuteronomy 32:9 according to
Gen 12:2 And I will make of you (Abram/Abraham) a great nation, and I will bless you and make your name great, so that you will be a blessing
or further along but definitions might be a better option
Hebrew
With regards to the ancient people, Hebrews are all twelve tribes, Israelites and Jews
Israelite
Pertaining initially to all twelve tribes but after the prophesied split of Solomon’s kingdom it refers to the Northern Ten Tribes plus any Levites living among them
Israelite’s in the latter sense are not Jews and cannot represent the Jewish people
Israelite in the former sense includes the Jews but is not formed entirely of Jews.
(Israelite in the sense of inhabitants of the land of Israel without specificity to tribal origin is also used, adding to the confusion).
Jew
Specific to the Southern Kingdom which consisted of Judah and Benjamin plus the Levites living among the Jews
A Jew is an Israelite and a Hebrew but a Jew does not represent ALL of Israel or ALL the Hebrew people
Samaritans
Initially The Northern Ten tribes were called Samaria though not Samaritans except for those who lived in the city of Samaria.
After captivity Samaritans were not pure bloodline of Israelite Northern Kingdom Hebrew but a mix of gentiles and Israelites but no Jews
Gentiles
Are typically indistinguishable from the Jews or they cannot trace their heritage back to the Jews. They might be able to trace their heritage back to the Northern Ten Israelite tribes but to the Jew this is irrelevant
Proselyte
One who came under the umbrella of the Jews by adoption/conversion. Proselytes included gentiles but also those from Israel of the Northern Ten Tribes that were not Jews.
Introduction
I’ve answered this subject in multiple different ways on this stack. This latest response is very important though I will probably repeat it again in this response and probably add links to other previous related responses.Romans 7 the law of the first husband
History
Israel typically twelve tribes. God marries Israel and enters into covenant with Israel
“"When I passed by you again and saw you, behold, you were at the age for love, and I spread the corner of my garment over you and covered your nakedness; I made my vow to you and entered into a covenant with you, declares the Lord God, and you became mine.”
Ezekiel 16:8
Fast forward
Rehoboam loses ten tribes and Israel is split into two kingdoms, the Northern ten tribes also called Israel and later Samaria and the Southern two tribes also called Judah from which we get the name Jews or Jewish despite it being Judah and Benjamin plus Levites.
“And when all Israel saw that the king did not listen to them, the people answered the king, "What portion do we have in David? We have no inheritance in the son of Jesse. To your tents, O Israel! Look now to your own house, David." So Israel went to their tents.
"Say to Rehoboam the son of Solomon, king of Judah, and to all the house of Judah and Benjamin”
1 Kings 12:16, 23
Notice the text calls Israel everyone except the house of David which are the two tribes Judah and Benjamin plus the rest of the people or the Levites.
Israel however is given a certificate of divorce
“Thus says the Lord: "Where is your mother's certificate of divorce, with which I sent her away? Or which of my creditors is it to whom I have sold you? Behold, for your iniquities you were sold, and for your transgressions your mother was sent away.” Isaiah 50:1
And
“And I saw that for all the adulteries of faithless Israel, I had sent her away and given her a writ of divorce, yet her treacherous sister Judah did not fear; but she went and was a harlot also.” JEREMIAH 3:8
Judah did not get a certificate of divorce because of multiple reasons including the promise to David that he would always have an heir on the throne.
The Jews or Judah goes into captivity and after seventy years a portion return to the land of Israel.
What is most important to note is that the Northern Ten Tribes never return back, the Samaritans are not accepted among the Jews because they mixed with the gentiles and as far as the Samaritans or Israelites from the Northern Kingdom who never returned back to the land they were one with the gentiles because they had been given a certificate of divorce.
Romans - Paul explains the saving of all of Israel.
The issue for the Christian Jews is a real one because among the gentiles there are now living and mixed into their bloodlines the blood of the divorced Ten Northern Tribes and according to the Law God CANNOT break His own Law.
“then her former husband who sent her away is not allowed to take her again to be his wife, since she has been defiled; for that is an abomination before the LORD, and you shall not bring sin on the land which the LORD your God gives you as an inheritance.” Deuteronomy 24:4
This was a serious issue for the early Church comprised of Jews only and proselytes. The Jews could accept a person to become a Christian if they first became a Jew. That didn’t sit well with those who knew their heritage was neither of Judah nor of Benjamin but of one of the other ten tribes.
By bloodline they were of Israel. Legally they could not re-enter into covenant with the God that divorced them
Law of the first husband.
Apostle Paul explains that the wife is bound to her first husband so long as the first husband is alive. But if the first husband dies, she is released from the law of the first husband and is free to marry without committing adultery.
“For a married woman is bound by law to her husband while he lives, but if her husband dies she is released from the law of marriage.”
Romans 7:2
(I understand that it’s contested who the Angel of the Lord is, but for the sake of brevity it’s Jesus prior to incarnation. He was the one that entered into covenant with ALL of Israel Acts 7:38 and He divorced the Ten Tribes)
Apostle Paul is saying that since Jesus the first husband died, He released the divorced Ten Tribes from the Law of marriage and opened the way for everyone to enter into the NEW COVENANT. Because not only did He die but He resurrected and became the eligible bachelor again, making Himself available as the Bridegroom.
New Covenant
The New Covenant is not of bloodlines. That’s why Apostle Paul says
“But it is not as though the word of God has failed. For not all who are descended from Israel (bloodline) belong to Israel (New Covenant Commonwealth),
This means that it is not the children of the flesh who are the children of God, but the children of the promise are counted as offspring.”
Romans 9:6, 8
According to the Bible the Church is Israel or a continuation of Israel, children of the promise not of the flesh but of faith. The Jews or the older brother in the prodigal son chose to stay outside but Paul is saying that the Jews will stay outside only for a while for all of Israel will be saved.
“remember that you were at that time separated from Christ, alienated from the commonwealth of Israel and strangers to the covenants of promise, having no hope and without God in the world.”
Ephesians 2:12
The Ten Tribes which have bloodlines to Israel are Gentiles because they had been cut off and they were for all intents and purposes Gentiles as many did mix with the Gentiles and they lost their bloodline identity though it was cut off.
However these bloodline Israelites come into the NEW covenant together with the gentiles under a New and BETTER way.
“But now in Christ Jesus you who once were far off have been brought near by the blood of Christ.”
Ephesians 2:13
The New Covenant makes the Old Covenant obsolete. Hebrew 8:13 This goes hand in hand with what Apostle John says.
“who were born, not of blood nor of the will of the flesh nor of the will of man, but of God.”
John 1:13
It’s not about bloodlines anymore, it’s about being IN HIM, in Jesus Christ.
Prophecy fulfilled
This age old prophecy that claimed God will accept the divorced Ten Tribes becomes fulfilled in Christ via the cross and the issue of the law of the first husband is resolved also in the cross
“Yet the number of the children of Israel shall be like the sand of the sea, which cannot be measured or numbered. And in the place where it was said to them, "You are not my people," it shall be said to them, "Children of the living God." And the children of Judah and the children of Israel shall be gathered together, and they shall appoint for themselves one head. And they shall go up from the land, for great shall be the day of Jezreel.”
Hosea 1:10-11
Notice that the distinction is made, Israel AND Judah (Jews). But they are now one, gathered together again. Israel who were not his people anymore but one with the gentiles are now children of God or Christians if you will.
And so in the New Covenant the New Israel is ALL of Israel twelve tribes not just the Jews or two tribes.
“James, a servant of God and of the Lord Jesus Christ, To the twelve tribes in the Dispersion: Greetings.”
James 1:1
James is addressing the ecclesia or the Church by its other name, the twelve tribes. The church is The New Israel, the Israel of God, of promise and not of the flesh.
“For he finds fault with them when he says: "Behold, the days are coming, declares the Lord, when I will establish a new covenant with the house of Israel and with the house of Judah,”
Hebrews 8:8
Again both Israel and Judah is mentioned in the New Covenant which was signed in blood at the cross. Covenant requires blood.
“And as for all who walk by this rule, peace and mercy be upon them, and upon the Israel of God.”
Galatians 6:16
Conclusion
The bloodline Israelites are all saved in the sense that all twelve tribes have access again to the New Covenant and this is opened to everyone Jew or Gentile (mixed with Israelite/Hebrew bloodlines).
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I think it’s important to acknowledge that gentiles were present throughout the whole process of deliverance from Egypt. They experienced the plagues, they went through the Red Sea, entered the covenant at Mt Sinai with the rest of Israel and so forth.
“A mixed multitude also went up with them, and very much livestock, both flocks and herds.”
Exodus 12:38
The gentiles always played a role in attaching themselves to the promises of God because after all, “all the nations of the world would be blessed in this seed”
“For the Lord will have compassion on Jacob and will again choose Israel, and will set them in their own land, and sojourners will join them and will attach themselves to the house of Jacob.”
Isaiah 14:1
It’s also fascinating to note that this language of ALL is used about the gentiles but yet Paul uses it about Israel.
“As for the word that he sent to Israel, preaching good news of peace through Jesus Christ (he is Lord of all),”
Acts 10:36
It’s always been about Israel. Israel has not been replaced, Israel is ongoing and the nations/gentiles attach themselves to the Israel of promise
“When they heard these things they fell silent. And they glorified God, saying, "Then to the Gentiles also God has granted repentance that leads to life."”
Acts 11:18
The current fight between the Church and the Jews is a fight of ignorance between two brothers the older brother of the Jews/Judah and the prodigal son Efraim, the younger brother that returns and is accepted not on merit but grace through faith which is the Church. The older brother is invited to come and join the feast and stop going about in the Old Covenant ways.
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Also worth mentioning that God was set from before He split up the nations at Genesis 11 Tower of Babel according to Deuteronomy 32:8ESV DSS LXX that He would once again regain all the nations. This is why it’s particularly important to see Acts 2 and the tongues of fire as well as the many nations being converted all at once.
This was a prophecy that God fulfilled from Psalm 82:8
“Arise, O God, judge the earth; for you shall inherit all the nations!”
Psalms 82:8
And it’s particularly interesting to see that God judges the one who disturbed the nations as Jesus Himself said that satan has already been judged John 16:11
This was also prophesied in Isaiah 14 and it says that the gentiles would attach themselves to Israel
“For the Lord will have compassion on Jacob and will again choose Israel, and will set them in their own land, and sojourners will join them and will attach themselves to the house of Jacob.”
Isaiah 14:1
God split the nations, set up his own nation and through that nation promised to Abraham, Isaac and Jacob He takes back all the nations including the ten divorced tribes that intermingled with the gentiles. And this by the cross. It’s no wonder even the heavenly hosts marvel at God’s ability to execute His plans and make it known ahead of time
In light of
“not all who are descended from Israel belong to Israel,”
Romans 9:6
And in light of the New Covenant revelation of the true sons of God awaiting the redemption of their bodies through adoption otherwise known as glorification
“And not only the creation, but we ourselves, who have the firstfruits of the Spirit, groan inwardly as we wait eagerly for adoption as sons, the redemption of our bodies.”
Romans 8:23
But technically since not all who are descended from Israel belong to Israel, only those of the promise by faith, then technically every individual who makes up the true Israel through personal, voluntary, non compulsive faith in Jesus Christ, this means that all of Israel will be saved. The true Israelites, all of them. They will be given supernatural bodies technically making super-physical. So yes all physical Israel that is the true Israel who enter into Christ by faith all will be saved and they are now part of the commonwealth of Israel, all twelve tribes.