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.’
[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.” Now here is something important to take in consideration. Notice that the verse 26 of Romans 11 is the Greek version of Isaiah 59:20 that says: Isaiah 59:20 ESV [20] “And a Redeemer will come TO Zion, to those in Jacob who TURN from transgression,” declares the Lord. The original verse in Hebrew is a bit different from the written Greek version. Here is saying in fact that NOT ALL Israel will be saved. Only a REMNANT of Israelites who REPENT will be saved at the coming of the Messiah and Redeemer.
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.”
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.
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