Romans 11:25-26 seems difficult for us to understand what it is all talking about.
First, the context of Romans chapter 11 talking about salvation.
Does God forsake people(Jews)? No. He never forsake them. He still promise to his people for the salvation. This is the covenant, that He already promised to Abraham of Genesis chapter 12.
Jews are part of the tree(Israel). It is not speak of flesh, but spiritual.
Genesis chapter 12 is not talking about flesh or nation, it is talking about spiritual with the promise of salvation which through Jesus Christ. Neither Genesis 12 focus on Jews only. Genesis 12 is speak of the world, that Christ died for the whole world according to 1 John 2:2.
God removed Jews from the tree, because of their unbelief- Romans 11:19-20. But, Jews, who are remain on the same tree, because of their faith. This is speak of their spiritual, not physical or nation, but their spiritual of salvation.
God removed Jews from the tree, because of their unbelief. God added Gentiles unto the tree join with believing Jews together, which are in Christ Jesus.
'Israel' of Romans 11:25 is not talking about physical or nation, it is talk about God's citizenship relate as salvation which is in Jesus Christ.
Romans 11:25 doesn't suggest, that there shall be re-establish of the covenent with Jews at the second coming FOR the 'millennial kingdom'. This verse tells us, about the RESULT of Gentiles and Jews both are reconciled together into one which are through in Jesus Christ according Ephesians chapter 2 by through Calvary.
To my understanding of Romans 11:25 interprets of 'And SO all Israel shall be saved' means: SO, that all PEOPLE shall be saved. Israel simple means God's people-either Jew or Gentile whosoever believeth in Christ, are God's elect.
I have study on Genesis 32:28 about 'Israel'. I found Genesis 32:28 have a refer verse. I am sure that most of you might not agree with me. I found there is a refer verse of Genesis 32:28, finds in Matt. 16:18-19. I realized there are three important keys for Israel & Church on the comparing of Genesis 32:28 & Matt. 16:18-19. I think, many Christians seem not get it what Christ said to Peter about Church, also, as what Christ told to Jacob about his name.
First, when Christ wrestled with Jacob, He asked Jacob, what's his name? Jacob told Him, 'Jacob'. Then, He told him, his name 'Jacob' no more, his name changed to 'Israel'. My understanding the meaning of Israel as what Christ said to him.
Let's read Genesis 32:28 as what Christ told Jacob: "...Thy name shall be called no more Jacob, but 'Israel' (Why? The meaning of Israel explains-) FOR as a prince hast thou power with God and with men, and hast prevailed."
Israle means, God given His power to His people, and they shall be successful or victory.
'Men' of Gensis 32:28 does not saying, they are 'Jews'. ALSO, it does not always focus on males, neither it saying, women are excluded from Israel. 'Men' means, people. Even, it doesn't saying, Gentiles are excluded from Israel either.
I find Matt. 16:18-19 have refer with Genesis 32:28. How do I know? There are three important key words as what Christ told Peter.
Christ said to Peter, "...That thou art Peter, and upon this rock I will build my church; and the gates of hell shall not prevail against it. And I will give unto thee the keys of the kingdom of heaven: and whatsoever thou shalt bind on earth shall be bound in heaven: and whatsoever thou shalt loose on earth shall be loosed in heaven."
There are three important key words of Matt. 16:18-19: 1. church 2. prevail 3. keys.
To my understanding of Matt. 16:18 - "I will build my church", means, Christ will build his PEOPLE. Church is not building, neither it is a religion. It means people. Christ doesn't saying church is for the Jews only. Church is for everyone whosoever believeth in Jesus Christ.
My understanding of 'the gates of hell shall not prevail against it.' Means, Satan, and the world cannot destroy God's people.
Why? Christ answered of Matt 16:19- "And I will give unto thee the KEYS of the kingdom of heaven..." Word, 'keys', they do not take into literal or physical. But it speaks of spiritual meaning. Christ told Peter, that He promised him, that He shall give the power to him, and his people to spread the gospel over the world.
Matt. 28:18-20- Christ told them, He shall give the POWER to his people, to spread the gospel over the world.
Acts 1:8 - Christ told them, that they shall receive the power from the above, to spread the gospel over the world.
Israel of Genesis 32:28 means, Christ gives the power to His people, and shall have victory.
Church of Matt. 16:18-19 means, Christ gives the power to His people, and they shall have victory.
Both Church & Israel are same meaning. By the way, I am NOT 'Replacement Theology'. Church does NOT replaced Israel. Christ already built his church thousands years before Calvary! Church in Greek word- 'Ekklesia' means, called out, or congregation.
Abraham was already part of the church in his time, because he was called out by the Lord. Just same as we are called out by Christ, for to be spearated from the world.
Israel of the New Testament is not a physical nation, or for the Jews only. Israel of the New Testament is a spiritual family of God, both Jew & Gentile whosoever believeth in Jesus Christ, are God's people.
Romans 11:25 explains when the result of Calvary, both Gentiles and Jews are all saved because of Jesus Christ already came out of Zion, the deliver to forgived all our sins away.
Zion of Romans 11:25 is speaks of heaven also, New Jerusalem. Christ came out of the heaven, came to earth, and he died on the cross for our sins. That's how Christ saved us, and already make reconciled both Jews and Gentiles unity into ONE body of Christ - Ephesians chapter 2.
Notice next verse - Romans 11:27 says that Christ already make the covenant with us, that He shall take our sins away, as he already fulfilled it of Matt. 26:27-28 & Daniel 9:27 by through Calvary by His blood.
By the way, Matt. 26:29 - "until THAT DAY when I drink it new with you in my Father's kingdom", does not saying, that Christ shall not drink it again with us TILL the "millennial kingdom" comes. Because Christ doesn't saying it is 'a thousand years'. Matt. 26:29 speaks of the second coming, and He shall bring an eternality kingdom upon earth, everything will be all new according to Romans 8:19-23.
The main idea of Romans chapter 11 focus on SALVATION for everyone because of the result of calvary. Romans chapter 11 does not discuss about millennial kingdom, because this passage doesn't saying 'a thousand years'. Romans 11:25-27 speak of our currently result because of the Calvary. Right now, more and more Gentiles are continuing adding unto the tree join with believeing Jews, even, many Jews are continue become saved and are adding unto the tree too. SO, all Israel shall be saved will be completed shall be at the second coming. Right now. Christ is still built his people, as he is continuing adding more people join into his family daily since early church history to today, and he will finish it at the second coming.
I hope that you understand what Apostle Paul was talking about of Romans chapter 11.
In Christ
Rev. 22:20 -Amen!