"What define a person as a Jew instead of a Gentile or vice versa?"
Dear sister Angela, please read ROMANS 2: 28-29 and you will find the very answer of your question above.
Dear sister, please, read my blog post entitled “WHAT IS YOUR STANDARD OF JUSTICE?”
This is below an excerpt of it.
Of course, God has chosen Israel. It is so said the Bible. I do not deny this fact.
But, the problem lies in the fact that you have not yet received the revelation of the mystery about which
Brother Paul was talking in the passage of Romans 11 that you’ve quoted.
Indeed, Brother Paul said:
"For I would not, brethren, that ye should be ignorant of this mystery, lest ye should be wise in your own conceits; that blindness in part is happened to Israel, until the fulness of the Gentiles be come in..."
"...blindness in part is happened to Israel, until the fulness of the Gentiles be come in..."
Do you believe this mystery?
I also know that, according to the Holy Scriptures that”…not all who are descended from Israel are Israel (Romans 9:6).
The Bible also declares that only the remnant will be saved (Romans 9:27).
“Isaiah cries out concerning Israel:
"Though the number of the Israelites be like the sand by the sea, only the remnant will be saved”
Indeed, Jesus-Christ did ask His disciples to go towards the lost sheep of Israel (Matthew 10:6) towards which Himself was sent (Matthew 15:24, Acts 13:23).
However, during the time of THE GRACE, Israel is partially hardened with the message of the Gospel, but later all true Israel will be saved. If you are really a true Hebrew Israelite, then you are my brother. Amen!
“…Israel is partially hardened with the message of the Gospel…”
Perhaps some Hebrews are implying since the Savior was Jewish, they themselves are special people in God's sight. In contrast, God wants all to know the following:
“A man is not a Jew if he is only one outwardly, nor is circumcision merely outward and physical. 29No, a man is a Jew if he is one inwardly; and circumcision is circumcision of the heart, by the Spirit, not by the written code. Such a man's praise is not from men, but from God”.
Hence, in this manner all true Christians are this type of Jew because their hearts have been circumcised by God's Spirit. This is what the greatest example of Christianity ever produced wrote, who also happened to be of Hebrew descent.
Moreover, consider what John the Baptist said to Jewish people in his day who thought they were special because of their nationality:
“But when he saw many of the Pharisees and Sadducees coming to where he was baptizing, he said to them: "You brood of vipers! Who warned you to flee from the coming wrath? 8Produce fruit in keeping with repentance. 9And do not think you can say to yourselves, 'We have Abraham as our father.' I tell you that out of these stones God can raise up children for Abraham”.
Today again there is a differentiation to be made between the true Jews, and the synagogue of Satan.
“I know your afflictions and your poverty-yet you are rich! I know the slander of those who say they are Jews and are not, but are a synagogue of Satan.
I will make those who are of the synagogue of Satan, who claim to be Jews though they are not, but are liars- I will make them come and fall down at your feet and acknowledge that I have loved you.
“…blindness in part is happened to Israel, until the fulness of the Gentiles be come in…”
Do you understand this mystery?
Do you believe that gentiles have also been chosen by the same God?
“Even us, whom he also called, not only from the Jews but also from the Gentiles? 25As he says in Hosea: "I will call them 'my people' who are not my people; and I will call her 'my loved one' who is not my loved one,"[a] 26and, "It will happen that in the very place where it was said to them, 'You are not my people,' they will be called 'sons of the living God”.
“…But you are a chosen people, a royal priesthood, a holy nation, a people belonging to God, that you may declare the praises of him who called you out of darkness into his wonderful light. Once you were not a people, but now you are the people of God; once you had not received mercy, but now you have received mercy”.
1 Peter 2:9-10
Believers in Christ are children of promise, children of the free woman:
“Now you, brothers, like Isaac, are children of promise. 29At that time the son born in the ordinary way persecuted the son born by the power of the Spirit. It is the same now. 30But what does the Scripture say? "Get rid of the slave woman and her son, for the slave woman's son will never share in the inheritance with the free woman's son."[a] 31Therefore, brothers, we are not children of the slave woman, but of the free woman”.
They are God's temple. Amen!
“Don't you know that you yourselves are God's temple and that God's Spirit lives in you?”
1 Corinthians 3:16
WE ARE ALL ONE IN CHRIST JESUS.
“ for all of you who were baptized into Christ have clothed yourselves with Christ. 28There is neither Jew nor Greek, slave nor free, male nor female, for you are all one in Christ Jesus. 29If you belong to Christ, then you are Abraham's seed, and heirs according to the promise”.
All those who are in Jesus Christ, namely Jews and Greeks ARE SAVED BY GRACE, THROUGH FAITH.
“For it is by grace you have been saved, through faith - and this not from yourselves, it is the gift of God - not by works, so that no one can boast. 10For we are God's workmanship, created in Christ Jesus to do good works, which God prepared in advance for us to do”
Ephesians 2: 8-10
Indeed, Brother Paul said:
“For we maintain that a man is justified by faith apart from observing the law”
“What then shall we say? That the Gentiles, who did not pursue righteousness, have obtained it, a righteousness that is by faith; but Israel, who pursued a law of righteousness, has not attained it. Why not? Because they pursued it not by faith but as if it were by works. They stumbled over the "stumbling stone." As it is written: "See, I lay in Zion a stone that causes men to stumble and a rock that makes them fall, and the one who trusts in him will never be put to shame”.
If you are not in Christ, then this doesn’t concern you!
So, please, stop bothering and troubling gentile believers.
Please, bear this in your mind once for all!