There is only one Lord Jesus Christ and there is only one body of the Lord Jesus Christ, the church.
The church is not the sum total of the local assemblies and national denominations. There may be a relationship but that is about all there is.
The early church was made up of saved Jews and saved Gentiles. They were saved the same way.
“In him we have redemption through his blood, the forgiveness of sins, in accordance with the riches of God's grace that he lavished on us with all wisdom and understanding.” Ephesians 1:7, 8
“And you also were included in Christ when you heard the word of truth, the gospel of your salvation. Having believed, you were marked in him with a seal, the promised Holy Spirit, who is a deposit guaranteeing our inheritance until the redemption of those who are God's possession—to the praise of his glory.” Ephesians 1:13, 14
Verses seven and eight are talking about Jews and 13 and 14 about the Gentiles.
Peter in Acts 15 says that the Gentiles were saved just like the Jews were saved.
“God, who knows the heart, showed that he accepted them by giving the Holy Spirit to them, just as he did to us. He made no distinction between us and them, for he purified their hearts by faith.” Acts 15:8, 9
Then he says that the Jews are saved just like the Gentiles are saved.
“No! We believe it is through the grace of our Lord Jesus that we are saved, just as they are.” Acts 15:11
This is wonderful. I am saved like you are saved and you are saved just like I am saved.
“If anyone is confident that he belongs to Christ, he should consider again that we belong to Christ just as much as he.” 2 Corinthians 10:7
“You, however, are controlled not by the sinful nature but by the Spirit, if the Spirit of God lives in you. And if anyone does not have the Spirit of Christ, he does not belong to Christ.” Romans 8:9
“The body is a unit, though it is made up of many parts; and though all its parts are many, they form one body. So it is with Christ. For we were all baptized by one Spirit into one body—whether Jews or Greeks, slave or free—and we were all given the one Spirit to drink.” 1 Corinthians 12:12, 13
“Make every effort to keep the unity of the Spirit through the bond of peace. There is one body and one Spirit—just as you were called to one hope when you were called— one Lord, one faith, one baptism; one God and Father of all, who is over all and through all and in all.” Ephesians 4:3-6
The church is made up of the saved.
The church is defined by saved people; people who are indwelt with the Holy Spirit or as in Colossians 1:27. “To them God has chosen to make known among the Gentiles the glorious riches of this mystery, which is Christ in you, the hope of glory.”
If you do not know that you are saved then you do not know that you are members of the real church of Jesus Christ.