Galatians 3:28 There is neither Jew nor Gentile, neither slave nor free, nor is there male and female, for you are all one in Christ Jesus.
Mercy_Shown, Saul is writing to Jewish Christians, his brethren. The whole of New Covenant writings except two personal letters to Tim, are written to Jewish Christians who founded home church fellowships in the places and locations he and the others (Pete, John, James) writes to.
If Gentiles are mentioned there is greater chance he is speaking about circumcised Gentile proselytes for they would be in the synagogues when many of the 3000 Jews born-again Jews at the Feast of Harvest returned to their synagogues and homes in Gentile lands taking with them an outline of Peter's sermon, their experiences with the Holy Spirit of Promise, and Jesus Messiah and told of their experiences at the feast. There are 17 languages the disciples speak in Acts 2 and those languages identify the areas or regions these Jews came from to the Feast for God was speaking to THEM. And that was only 3000 saved on the Day of Pentecost. If 3000 is a median number, then by weeks end God the Holy Spirit baptized into the body of Christ about 21,000 Jews and filled them with the Holy Spirit of Promise God made to Israel. The New Covenant writings contain Jewish history, the Law of Moses, the Abrahamic Covenant, their prophets and prophecies, their culture, their Judaic religion and practices of Temple and Tabernacle life. They quote extensively out of the Law, Psalms, and Prophets and these writings are addressed to Jewish Christians.
Now, to your Scripture: Take note for the things the writers - all of them - write about no hard-core, uncircumcised, non-covenant Gentiles coming out of their places of worship of these dumb idols would have the level of knowledge in order to understand all the Jewishness of the New Covenant writings.
6 I marvel that ye are so soon removed from him that called you into the grace of Christ unto
another gospel:
7 Which is not another; but there be some that trouble you, and would pervert the gospel of Christ.
8 But though we, or an angel from heaven, preach any other gospel unto you than that which we have preached unto you, let him be accursed. Gal. 1:6–8.
The "another gospel" Saul is referring to is Judaism. Hebrew 6 also addresses Jewish Christians due to persecution and excommunication from their Jewish brethren for the testimony of Christ wanted to return to Judaism, but Saul says, "It is impossible once they had been enlightened."
Another deep abiding concern the Jewish Christians had that Saul writes to and addresses was the effect Israel's Messiah had on the existing covenants, specifically the Abrahamic Covenant.
19 Wherefore then serveth the
law? It was added because of transgressions, till the
seed should come
to whom the promise was made; and it was ordained by angels in the hand of a mediator.
20 Now a mediator is not a mediator of one, but God is one.
21
Is the law then against the promises of God? God forbid: for if there had been a law given which could have given life, verily righteousness should have been by the
law.
22 But the scripture [Jewish Scriptures] hath concluded all under sin, that the promise by faith of Jesus Christ might be given to them that believe.
23 But before faith came,
we [Jews] were
kept under the
law, shut up unto the faith which should afterwards be revealed.
24 Wherefore the law was
our [Jews] schoolmaster to bring
us [Jews] unto Christ, that
we [Jews] might be justified by faith.
25 But after that faith is come,
we [Jews] are no longer under a schoolmaster.
26 For
ye [Jews] are all the children of God by faith in Christ Jesus.
27 For as many of
you [Jews] as have been baptized into Christ have put on Christ.
28 There is neither Jew nor Greek, there is neither bond nor free, there is neither male nor female: for
ye [Jews] are all one in Christ Jesus.
29 And if
ye [Jews] be Christ’s, then are
ye [Jews] Abraham’s seed, and
heirs according to the promise [given to Abraham]. Gal. 3:19–29.
A Jewish Covenant. A Jewish Messiah. A New Covenant initiated by a Holy Spirit. Israel entered a new era and It took time for the Jews - especially experienced Jewish Christians - to search the Hebrew Scriptures to get an understanding as to the 'new thing' God was doing in Israel. And for at least four decades until the destruction of the Jewish Temple everything God was doing with regard to this New Covenant was being done to Israel.