Yet, if all have believed in Jesus? No matter what church they are in? Are all one body by God's decree.Salvation doesn't depend on membership in a church or group.
The body cells you have now have replaced the body cells of when you were younger. Same body, but more mature than the last! Likewise, those in the first church have died, only to be replaced by fresh members to replace them IN THE SAME BODY!
For in one Spirit we were all baptized into one body—Jews or Greeks, slaves or free
— and all were made to drink of one Spirit." 1 Cor 12:13
grace and peace .......