1 Corinthians 12:12 For as the body is one, and hath many members, and all the members of that one body, being many, are one body: so also is Christ.  
 
Paul is comparing the physical body to the Church, the members of the physical body and the members of the Church. Then he calls the Church, Christ. And it is Christ. It is the Body of Christ in a very real sense.  
 
God so loved the world, that is the cosmos, the universe and its order, that He gave His unique Son so that whoever believes into Him should not die but should have the life of the coming age, an uncreated life that does not end. And how do we believe into Him? It is "into" in the original language.

Well, who is Christ? Christ is the Head of the Body in Heaven, yes. Christ is also a many-membered Body here on Earth. When we serve each other, we do serve Him. When we build up each other, as you are doing, we build Him up. ! Corinthians 12::12 For as the body is one, and hath many members, and all the members of that one body, being many, are one body: so also is Christ. Paul is comparing the physical body to the Church, the members of the physical body and the members of the Church. Then he calls the Church, Christ. And it is Christ. It is the Body of Christ in a very real sense.

To believe into Christ, a person must first be born again. From that point, this person begins to believe Christ rather than believing all the teachings of men and evil spirits. As the Holy Spirit unfolds His revelation, the orders that are so clearly shown in the Bible become real and understandable to the believer. God speaks to every person all the time. We were created to be directed, as God utters His Word to us, and powered by the Holy Spirit from moment to moment. Most people don't listen at all. A remnant, a small company of believers, are beginning to learn to listen and respond in God's faith which comes as God utters His Word to us.

(some caveats about hearing God's Voice)

Believing into Christ is a process of:

 
1. discerning what is and what is not the Body of Christ,
 
2. and discerning what is and what is not your own particular place of service within this Body of Christ,
 
3. and finally to become what God created you to become in the Body of Christ.

The foundation of the Church must be laid first. First Christ, then the apostles built on Christ as foundation of the Church. These apostles were restored to the Church in the late 1940s. God has been restoring His Church to its original glory and purpose since it left God's pattern in the early centuries after Jesus ascended and gave gifts to men. May God bless you in this work.