Do Gentiles become Jews when they believe?

 As a believer (Gentile) you become part of the body of Christ, not Israel. You are a spiritual Gentile, not a Jew. Israel is a nation consisting of Jews, Hebrews are an ethnicity, who are from the linage of Abraham, Isaac and JACOB (the twelve tribes). A gentile (both believer and non believer) is from Abraham only, not Isaac and Jacob.

Being Abraham’s seed does not make one Jewish, this is where people have been taught wrong, its Abraham, Isaac and Jacob, (from whom came the 12 tribes) otherwise the Arabs are Jewish too. selah.

John 18:35 Pilate answered to Jesus, "Am I a Jew? Your own nation and the chief priests have delivered You to me.”

there are two groups of people the bible distinguishes, Gentiles and Jews.

Those who had the covenant delivered to them and became a theocracy under God those who have no covenant and do not know not God

It is written "that the Christ would suffer, that He would be the first to rise from the dead, and would proclaim light to the Jewish people and to the Gentiles" (Acts 26:23). Two groups of people are always distinguished, unless referred to the Church

Later it was Saul who was specifically called to this other group of people that was not his own while the original apostles worked among their people, the Jews. Paul was also going to the Jews first as his priority but they rejected the message from him and he said in Acts 28:28 "Therefore let it be known to you that the salvation of God has been sent to the Gentiles, and they will hear it!"

Rom. 11:12-13 “Now if their fall is riches for the world, and their failure riches for the Gentiles, how much more their fullness! For I speak to you Gentiles; inasmuch as I am an apostle to the Gentiles, I magnify my ministry. ” He spoke of himself as “a teacher of the Gentiles in faith and truth” (1 Tim. 2:7)

Paul made the distinction of Gentiles and Jews before their salvation and continued this distinction afterwards, in Rom.2:9,10. Yet he explained we are all united in Christ, in the new entity the church, which abides in the new covenant.

Speaking to the Gentiles, Gal 3:29 “And if you are Christ's, then you are Abraham's seed, and heirs according to the promise.” He refers to one being of the seed of Abraham when one exercises faith.

Under the new covenant

Rom. 10:12-13 “For there is no distinction between Jew and Greek, for the same Lord over all is rich to all who call upon Him. For "whoever calls on the name of the Lord shall be saved."

 He is not saying Jews and Gentile are no longer valid distinctions or erased, but that both call upon the Lord for the same salvation.

Rom 1:16 “For I am not ashamed of the gospel of Christ, for it is the power of God to salvation for everyone who believes, for the Jew first and also for the Greek.”

Greeks representing the Gentiles. The Bible makes a distinction of Jew and Gentile throughout is pages.

Paul had to rebuke Peter:

Gal 2:14 “But when I saw that they were not straightforward about the truth of the gospel, I said to Peter before them all, "If you, being a Jew, live in the manner of Gentiles and not as the Jews, why do you compel Gentiles to live as Jews?

 Clearly there were distinctions, yet he also said of those who were in the body of Christ to not see each other as they did before.

Col. 3:10-11 “and have put on the new man who is renewed in knowledge according to the image of Him who created him, where there is neither Greek nor Jew, circumcised nor uncircumcised, barbarian, Scythian, slave nor free, but Christ is all and in all.”

Gal 3:28 “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.”

What he is saying is that we as believers are all children of God, the body of Christ and that any differences should not be used to divide (2 Cor.12:13). Jew and Greek is a more specific substitute for the distinction of Jew and Gentile. There were still slaves and masters existing at the time just as there were still men and women. But this was to be overlooked in defining a person who is now in Christ.

In the same way Matt 19:6 "So then, they are no longer two but one flesh. “ Does not mean one literal person, but spiritually.

Jesus says Rv. 2:9 "and I know the blasphemy of those who say they are Jews and are not, but are a synagogue of Satan.

Clearly there were those who claimed to be Jews but were not believers and were against the Messiah (as in Acts 14:2).

The Gentiles as said to be called by his name (Acts 15) Acts 21:25 “Gentiles who believe”

Paul never said Gentiles were Jews after they believe.

But were grafted into the covenant made with Israel (Rom.11:17-24), so they should not boast as if God is through with Israel and her promises and replaced her with a church of Gentiles.Eph.2:11 explains the Gentiles who are in Christ are equal to the Jews in christ all having access by the same spirit.

Eph. 2:14-18 He has broken down the middle wall of separation, 15 having abolished in His flesh the enmity, that is, the law of commandments contained in ordinances, so as to create in Himself one new man from the two, thus making peace, and that He might reconcile them both to God in one body through the cross, thereby putting to death the enmity. And He came and preached peace to you who were afar off and to those who were near. For through Him we both have access by one Spirit to the Father.”

Eph. 3:6 that the Gentiles should be fellow heirs, of the same body, and partakers of His promise in Christ through the gospel”

Rom. 15:10-11 And again he says: "Rejoice, O Gentiles, with His people!"And again: "Praise the Lord, all you Gentiles! Laud Him, all you peoples!"

Gal 3:14 that the blessing of Abraham might come upon the Gentiles in Christ Jesus, that we might receive the promise of the Spirit through faith.”

Acts 17:17 Therefore he reasoned in the synagogue with the Jews and with the Gentile worshipers, and in the marketplace daily with those who happened to be there.”

Just as Gentiles were not called Jews when they worshiped God in the synagogue, they are not called Jews when they believe in the Messiah, Jesus. They are fellow heirs, they become believers, spiritual gentiles. This distinction continues through the Scripture.