The church is not Gentile! The first Christians were almost all Jewish. In any case, in Christ, there is neither Jew nor Gentile; we are all one in Him.
Saul was writing to Jewish Christians who had concern about the effect Messiah had on the Abrahamic Covenant.
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 [Jews] 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. Gal. 3:23–29.
Do you see Saul trying to explain to Jewish Christians at their Jewish home churches in Ephesus that everything is OK? Do you see the Jewishness of his letter to Jewish Christians? They worried at what it meant to be a Messiah-follower and how this affected their standing in the Abrahamic Covenant. Saul is not teaching a new covenant of Jews and Gentiles. There is NO NEW COVENANT in the New Covenant writings of Saul, or James, or Peter, or John. All their letters are spent discussing and explaining Messiah's effect on their Law, their Psalms, and their Prophets - their Judaic religion.
The New Covenant is between God and the House of Israel (northern kingdom) and the House of Judah (southern kingdom) - Jer. 31:31-34. There are no Gentiles mentioned nor are they included in the New Covenant. God is saving Gentiles without a covenant.
Israel is betrothed to God and is His Bride. Israel is the True Church of the Living God and the Church Jesus said He was going to build began at the Feast of Harvest (Pentecost) as a Jewish Church which is a continuation of the Church of God in the desert at the time of the Tabernacle, only they were called the "Great Congregation."
At the Marriage Supper Israel is there through Covenant.
Gentiles are there by invitation (Matt. 22.)
Throughout the Jewish Scriptures of the Law, the Psalms, and the Prophets which record the history of Israel's Redemption there is no place where God made covenant with Gentiles. None.