1. John taught us that ALL humans who do not believe in the Son of God are anti-Christ(ian). (1 John 2:22-23).
2. Paul taught that NOT ALL naturally-born descendants of Abraham, Isaac and Jacob are Israel (Romans 9:6-8), because those of the naturally-born descendants who do not believe in the seed of Abraham (Christ) are broken off from God's covenant-promises that He made with Abraham and his seed (Romans 11:1-5, 17).
They are broken off from the Israel of God. (Galatians 6:16).
3. Jeremiah said that God would not cut off ALL the seed of Israel when God brings in a New Covenant (Jeremiah 31:36-37), meaning that a remnant would be saved - just as occurred when Jesus had died and risen again (as Paul stated in Romans 11:1-5).
4. Paul taught us that Gentiles who do believe are grafted into Israel - into God's covenant-promises with Abraham and his seed - and are among the remnant of the naturally-born descendants of Abraham, Isaac and Jacob who believe. (Romans 11:17).
5. Peter and Paul both taught us that together these Jews and Gentiles in Christ are the living stones that are God's Tabernacle, indwelt by the Holy Spirit. (Ephesians 2:19-22; 1 Peter 2:5).
6. Paul taught that in Christ there is neither Jew nor Gentile. (Galatians 3:28).
7. Therefore simple arithmetic and logic tells us that the church = Israel = the church.
The Deliverer who came out of Zion is Jesus, and the day in which He made a (new) covenant with Israel was the day He took away their (and our) sins (Romans 11:26-27).
Ever since the Deliverer came out of Zion and made a new covenant with Israel in the day He took away their (and our sins):-
(a) The fullness of the Gentiles is being grafted into Israel through faith in Christ, sharing with the naturally-born believing descendants of Israel in the root and fatness of the Olive tree; and
(b) IF (Romans 11:23) an unbelieving Jewish person repents of his or her unbelief, the person will be grafted back into the Israel that he is a naturally born descendant of ("their own Olive tree") - and this is because:
i. For the sake of God's promise to Abraham, Isaac and Jacob, they are still loved. *
ii. God had mercy on Gentiles who believe through their unbelief.
iii. God is able to graft them in again.
"When the Lord Jesus is revealed from heaven with his mighty angels, with flaming fire He will mete out punishment on those who do not know God and do not obey the gospel of our Lord Jesus. They will undergo the penalty of eternal destruction, away from the presence of the Lord and from the glory of his strength, when he comes to be glorified among his saints and admired on that day among all who have believed - and you did in fact believe our testimony." -- 2 Thessalonians 1:7-10.
He said, "For God so loved the world, that he gave his only begotten Son, that whosoever believes in him should not perish, but have everlasting life. For God sent not his Son into the world to condemn the world; but that the world through him might be saved.
He that believes on him is not condemned: but he that believes not is condemned already, because he has not believed in the name of the only begotten Son of God. And this is the condemnation, that light has come into the world, and men loved darkness rather than light, because their deeds were evil." -- John 3:16-19.
* As concerning the election, the natural descendants of Abraham, Isaac and Jacob, a.k.a "Jews" - those who do not believe in Messiah - are beloved of God because of (God's) election of, and covenant promises with Abraham, Isaac, Jacob and their descendants, but as concerning the gospel, they are enemies, and because of this, believing Gentiles have been grafted into Israel (Romans 11:28).
Note: "Beloved" does not mean "saved".
"As concerning the gospel, they are enemies for your sakes: but as concerning the election, they are beloved for the father's sakes. For the gifts and calling of God are without repentance." -- Romans 11:28-29.
"For your sakes" and "for the fathers' sakes" [διά diá] is causal: it simply means "because of". So IF they repent of their unbelief, they will be grafted in again. For God is able to graft them in again.
However we should not ever overlook the fact that Jews who do not believe in Messiah are nevertheless beloved of God because of His election of, and covenant promises with Abraham, Isaac, Jacob and their descendants.
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