The children of God are not those who are born of a physical birth, but those who are reborn with a birth that comes from God through faith in his Son Jesus Christ (the Messiah), regardless of whether they are Jews or Gentiles:
John 1:11-13 ESV
[11] He [Jesus] came to his own [Israel], and his own people did not receive him. [12] But to all who did receive him, who believed in his name, he gave the right to become children of God, [13] who were born, not of blood nor of the will of the flesh nor of the will of man, but of God.
Jesus said once to the Jews who were not listening to him nor the words of God, that they didn't belong to God but to their father the devil, the father of lies. This clearly proves that not all Jews will be saved just because they are genetically Jews. Only those who sincerely believe that Jesus is the Lord and Messiah sent by God:
John 8:41-47 ESV
[41] (Jesus:) You are doing the works your father did.” They (the Jews) said to him, “We were not born of sexual immorality. We have one Father—even God.”
[42] Jesus said to them, “If God were your Father, you would love me, for I came from God and I am here. I came not of my own accord, but he sent me. [43] Why do you not understand what I say? It is because you cannot bear to hear my word.
[44] You are of your father the devil, and your will is to do your father’s desires. He was a murderer from the beginning, and does not stand in the truth, because there is no truth in him. When he lies, he speaks out of his own character, for he is a liar and the father of lies. [45] But because I tell the truth, you do not believe me. [46] Which one of you convicts me of sin? If I tell the truth, why do you not believe me?
[47] Whoever is of God hears the words of God. The reason why you do not hear them is that you are not of God.”
Moises talked to the Jewish people about the coming of another Prophet like him. In fact, he was talking about the coming of the Messiah. And he continued saying that any Jew who doesn't listen to the Messiah will be removed from being part of God's people:
Acts 3:22-23 ESV
[22] Moses said, ‘The Lord God will raise up for you a prophet (the Messiah) like me from your brothers. You shall listen to him in whatever he tells you. [23] And it shall be that every soul who does not listen to that prophet shall be destroyed from the people.’
The apostles Peter and John spoke with conviction and boldness when they were arrested by the Jewish religious leaders for healing a cripple man, saying that there is no salvation for Jews except by believing in Jesus the Messiah:
Acts 4:11-12 ESV
[11] This Jesus is the stone that was rejected by you (the Jews), the builders, which has become the cornerstone. [12] And there is salvation in no one else, for there is no other name under heaven given among men by which we must be saved.”
Jewish people's minds were hardened and that's why they cannot understand the truth of God's Word when they read the Scriptures to this day. But as soon as they believe and turn to the Lord Jesus, the veil in their eyes will be lifted:
2 Corinthians 3:14-16 ESV
[14] But their (Jewish people) minds were hardened. For to this day, when they read the old covenant, that same veil remains unlifted, because only through Christ is it taken away. [15] Yes, to this day whenever Moses is read a veil lies over their hearts. [16] But when one turns to the Lord [Jesus], the veil is removed.
The apostle Paul explains in Romans chapter 9 that the Gentiles, who were not following God's Law, were made right with God because of their faith in Jesus. But the Israelites, who were keeping the Law, were not made right with God for not trusting in the Messiah:
Romans 9:30-33 ESV
[30] What shall we say, then? That Gentiles who did not pursue righteousness have attained it, that is, a righteousness that is by faith; [31] but that Israel who pursued a law that would lead to righteousness did not succeed in reaching that law.
[32] Why? Because they did not pursue it by faith, but as if it were based on works. They have stumbled over the stumbling stone (the Messiah), [33] as it is written, “Behold, I am laying in Zion a stone of stumbling, and a rock of offense; and whoever believes in him will not be put to shame.”
The apostle Peter writes that when we (whether Jews or Gentiles) believe and come to Jesus—who is the living cornerstone of God's temple, rejected by his people, but chosen by God for great honor—, we are then transformed into living stones, chosen people, and holy priests of God the Father, to offer him continual spiritual sacrifices through the mediation of Jesus, his Son and Messiah:
1 Peter 2:4-8 ESV
[4] As you come to him (Jesus), a living stone rejected by men but in the sight of God chosen and precious, [5] you yourselves like living stones are being built up as a spiritual house, to be a holy priesthood, to offer spiritual sacrifices acceptable to God through Jesus Christ.
[6] For it stands in Scripture: “Behold, I am laying in Zion a stone, a cornerstone chosen and precious, and whoever believes in him will not be put to shame.”
[7] So the honor is for you who believe, but for those who do not believe, “The stone that the builders rejected has become the cornerstone,” [8] and “A stone of stumbling, and a rock of offense.” They stumble because they disobey the word, as they were destined to do.
The complete remnant of Israelites will be saved after the complete remnant of Gentiles has been saved
Paul writes in Romans 11:25-26 that “some of the people of Israel (those who have yet to repent and be saved by faith in Christ Jesus) have hardened their hearts.” But they will be saved after the number of the Gentiles (the remnant of non-Israelites who repent and are saved by faith in Jesus) has come in. That is why Paul goes on to say that “then all Israel (the whole remnant of Israelites who repent and believe in Christ) will be saved.” And then he adds that God has not rejected the people of Israel, because He chose the ancestors Abraham, Isaac, and Jacob. (Romans 11:1-10, 28-29)
Romans 11:25-27 ESV
[25] Lest you be wise in your own sight, I do not want you to be unaware of this mystery, brothers: a partial hardening has come upon Israel, until the fullness of the Gentiles has come in. [26] And in this way all Israel will be saved, as it is written, “The Deliverer will come from Zion, he will banish ungodliness from Jacob”; [27] “and this will be my covenant with them when I take away their sins.”
Not all Israel will be saved. Only a REMNANT of Israelites will repent and be saved, just as only a remnant of Gentiles will repent and be saved. In fact, Paul says in Romans 9:26, quoting the prophecy of Isaiah 10:22, that “though the children of Israel are as numerous as the sand on the seashore, only a REMNANT will be saved.”
Here is a good passage in Micah 2:12 which confirms and clarifies what Paul was referring in Romans 11:26 that “all Israel will be saved”, which in fact is saying that ALL the REMNANT of Israel who repent and believe in Christ will be saved:
Micah 2:12 ESV
[12] I will surely assemble ALL of you, O Jacob; I will gather the REMNANT of Israel; I will set them together like sheep in a fold, like a flock in its pasture, a noisy multitude of men.
Paul continues writing in Romans chapter 11:
Romans 11:28-32 ESV
[28] As regards the gospel, they are enemies for your sake. But as regards election, they are beloved for the sake of their forefathers. [29] For the gifts and the calling of God are irrevocable. [30] For just as you were at one time disobedient to God but now have received mercy because of their disobedience, [31] so they too have now been disobedient in order that by the mercy shown to you they also may now receive mercy. [32] For God has consigned all to disobedience, that he may have mercy on all (Jews and Gentiles).
Here above it says that God will have mercy on ALL, yes, whether they are Jews or Gentiles. But this doesn't mean that all Gentiles and Jews will be saved. Only those of poor spirit, the meek, the merciful, who hunger and thirst for righteousness, the pure in heart, and the peacemakers will be saved and called children of God. (See Matthew 5:1-9.) Only those whether Jews or Gentiles who believe and receive Jesus Christ as their Lord and personal Savior, will be adopted as children of God. (See John 1:12-13; Romans 10:8-13.)
When will the complete remnant of Gentiles and Israelites be saved?
The following verses confirm that this will take place at the moment of the Rapture just after the Great Tribulation or Anguish perpetrated by the Antichrist, when EVERY PERSON in the world will SEE JESUS CHRIST coming from the clouds of heaven and mourn, including those who pierced or crucify him—the Jews.
Isaiah 59:20-21 ESV
[20] “And a Redeemer (Jesus) will come to Zion, to those in Jacob who turn from transgression (sin),” declares the Lord.
[21] “And as for me, this is my covenant with them,” says the Lord: “My Spirit that is upon you, and my words that I have put in your mouth, shall not depart out of your mouth, or out of the mouth of your offspring, or out of the mouth of your children’s offspring,” says the Lord, “from this time forth and forevermore.”
Zechariah 12:9-10 ESV
[9] “And on that day I will seek to destroy all the nations that come against Jerusalem.
[10] “And I will pour out on the house of David and the inhabitants of Jerusalem a spirit of grace and pleas for mercy, so that, when they look on me, on him (Jesus) whom they have pierced, they shall mourn for him, as one mourns for an only child, and weep bitterly over him, as one weeps over a firstborn.
Matthew 24:29-31 ESV
[29] “Immediately after the [great] tribulation of those days the sun will be darkened, and the moon will not give its light, and the stars will fall from heaven, and the powers of the heavens will be shaken.
[30] Then will appear in heaven the sign of the Son of Man (Jesus Christ), and then all the tribes of the earth will mourn, and they will see the Son of Man coming on the clouds of heaven with power and great glory. [31] And he will send out his angels with a loud trumpet call, and they will gather his elect [from all over the world], from the four winds [of the earth], from one end of heaven to the other.
Revelation 1:7 ESV
[7] Behold, he (Jesus) is coming with the clouds, and every eye will see him, even those who pierced (crucify) him, and all tribes of the earth will wail on account of him. Even so. Amen.
Revelation 14:9-16 ESV
[9] And another angel, a third, followed them, saying with a loud voice, “If anyone worships the beast (the Antichrist) and its image and receives a mark on his forehead or on his hand, [10] he also will drink the wine of God’s wrath, poured full strength into the cup of his anger, and he will be tormented with fire and sulfur in the presence of the holy angels and in the presence of the Lamb. [11] And the smoke of their torment goes up forever and ever, and they have no rest, day or night, these worshipers of the beast and its image, and whoever receives the mark of its name.”
[12] Here is a call for the endurance of the saints, those who keep the commandments of God and their faith in Jesus. [13] And I heard a voice from heaven saying, “Write this: Blessed are the dead who die in the Lord from now on.” “Blessed indeed,” says the Spirit, “that they may rest from their labors, for their deeds follow them!”
[14] Then I looked, and behold, a white cloud, and seated on the cloud one like a son of man (Jesus Christ), with a golden crown on his head, and a sharp sickle in his hand. [15] And another angel came out of the temple, calling with a loud voice to him who sat on the cloud, “Put in your sickle, and reap, for the hour to reap has come, for the harvest of the earth is fully ripe.” [16] So he who sat on the cloud swung his sickle across the earth, and the earth was reaped.
Christians must preach the Gospel to Jews and non-Jews now and wherever they are
There is no Scripture that says we must currently help Jews, so that they may believe and be saved, to return to the land that God had promised the Israelites in the Old Covenant or Testament. In fact, when Jesus the Messiah returns, everyone will see him coming, including Jews, wherever they are.
Revelation 1:5-7 NIV
[5] To him who loves us and has freed us from our sins by his blood, [6] to him who has made us to be a kingdom and priests to serve his God and Father—to him be glory and power forever and ever! Amen.
[7] Look, he is coming on the clouds! Everyone will see him with their eyes, even those who pierced him (the Jews). And all the peoples of the earth will mourn over him. So it will be! Amen.
The present-day Israel of God is not a physical land called Israel. Israel is actually God's chosen people from among Gentiles and Jews who repent of their sins and give their lives to Jesus the Messiah in baptism.
Galatians 3:26-29 NIV
[26] You are all children of God through faith in Christ Jesus, [27] for all of you who were baptized into Christ have clothed yourselves with Christ.
[28] There is neither Jew nor Greek, there is neither slave nor free, there is neither male nor female, for you are all one in Christ Jesus.
[29] And if you belong to Christ, then you are Abraham's offspring and heirs according to promise.
Jesus will return to reign for 1,000 years over the whole earth, not just over a small land like the present-day state of Israel. God does not need us to bring Jews to the physical land of Israel. This is not biblical, but simply a dogmatic biblical interpretation.
What God truly wants is for us to preach the Gospel of salvation in Jesus Christ to all the Jews we can, wherever they are. The Gospel is what the Jews need to hear so that some may be saved now. In fact, they must hear it now so that many may believe that Jesus is the Messiah when he comes and descends from the clouds.
Romans 10:14-17 NIV
[14] How then will they [the Israelites] call on him in whom they have not believed? And how will they believe in him of whom they have not heard? And how will they hear without someone preaching? [15] And how will they preach unless they are sent? For it is written: “How beautiful are the feet of those who bring good news!”
[16] However, not all Israelites accepted the good news. Isaiah says, “Lord, who has believed our message?”
[17] So faith comes from hearing the message [that is preached] and the message that is heard is the word of Christ.