He that believeth and is baptized shall be saved. He that believeth not shall be condemned. Others include belief, repentance, grace, and works of God. Peter mentioned that baptism didn't just wash filth from the body. I said that to clarify that Peter is speaking of water baptism here.
Many members compose it.
To name a few at the time the book of Corinthians was wrote, Paul mentioned apostles, prophets and teachers just to name a few. He then clarified how you become a member of the body of Christ. They say that the Spirit will come upon you as it did the Apostles in Acts 2. If this were true, King Agrippa would be a Christian, but even Agrippa knew better than that. I know that you do believe.