There is only one body, just as there is only one head. St. Paul was emphatic in his emphasis that we all be one, as in undivided. You admit that the early church's scriptures are God inspired, so it must have some validity. Did not ever notice that all of the different congregations in the Bible were listening to the instructions of one central group of people?
And yes, if one goes through their confirmation classes and states that he or she has faith that Jesus Christ is the only begotton son of God, the Messiah, through whom we may access the father, and through whom our salvation is sealed, then they are assumed to be "okay with God." I don't know of any other way a person can express their faith. What do you do in your church, aside from asking if the person is "saved?"