If you accept Christ as your savior, repent of your sins, get baptized, and receive the Holy Spirit, you are a
member of the church which is the body of Christ.
I do not believe that membership in a particular church organization such as the Catholic church is necessary for salvation.
The Catholic and Eastern Orthodox church both claim to be the one true church but I don't believe that the body of Christ is restricted to either one of these churches. The body of Christ encompasses all true Christians regardless of their particular church affiliation.
And I believe that the Holy Spirit can at any time raise up a body of believers that constitute a church of God.