The Church was 100% Jewish

The Church was mostly Jewish in its makeup for many years.
It was (and a denomination still is) the Nazarene sect of Judaism, the faithful remnant who followed Israel’s Messiah. The “church” is not something separate from Israel, but rather is the remnant of the faithful within Israel and includes every faithful Christian individual alive.

Isaiah pointed out that in times of Israel’s great apostasies, the faithful of the nation were reduced to a tiny remnant of elect ones. Isaiah 1:8-9

 So it was in the first century, where Paul identifies himself as an example of the faithful remnant. Romans 11:1-5
The apostles continually say that Christians; born again believers, are the true elect ones:  2 Timothy 2:10; Col. 3:12; Galatians 6:15-16; 1 Peter 1:2; 1 Peter 2:9-10

However, some people have a bizarre idea of who is Israel: counting the disobedient sons of Abraham as Israel while discounting entirely the sons of Abraham by faith.
 Paul said that when the Jewish nation rejected Christ, the true Israel was carried on not through the lineages of the wicked sons but rather through the obedient few (called the “remnant”), such as was true in Isaiah’s day, Romans 9:27-29 and Elijah’s day. Romans 11:3-5

Peter says the same thing at Acts 3:22-24, where it is clear that the wicked Jews who refuse Christ were to be “cut off from among the People of Israel” while the faithful Jews (John the Baptist, Joseph and Mary, the Twelve, the Seventy, the three thousand on Pentecost day, and many other Jews) were the True Faithful Israel.

The Israelite church was with Moses in the wilderness, Acts 7:37-38 And within a few years after Pentecost, the faithful Israelites learned how to start accepting both Jewish and also gentile followers from all over the empire to convert into their Nation. 1 Peter 2:9-10; Matthew 21:40-45  And so the remnant of true righteous Christian Israel have maintained the faith through this age, while a large portion of the established Church have lost the plot, to their eternal discredit.
And so it was also in Moses’ day, when the many thousands of wicked sons of Abraham were slain in the wilderness while the tested and tried sons of Abraham survived and got to enter the Promised Land. We must NEVER count the continuation of Israel through the wicked sons but rather always through the faithful remnant!

The real Church is the faithful Christians from every tribe, race, nation and language, Revelation 5:9-10;  they are the Israelites of God.  Israelites = the Overcomers with God.