According to New Testament teaching belonging to Christ and belonging to his body, the church, are inseparable. Jesus said, "I am the vine; you are the branches" (John 15:5). If we are part of him, we are also part of one another.
This involves a vital connection with him as the true vine. It is not enough simply to be on the official membership roll of your church, or even to have gone through some form of water baptism. These things only count if you are truly joined to Christ and abiding in relationship with him. The true church of Jesus Christ is made up of true followers of Christ.
Being a Christian in name only is one of the greatest problems for the Christian faith today. Many profess to believe in Christ, but do not even attend a place of fellowship. Others have contact with a church and go to services but have no real relationship with the Lord. These have a form of religion but deny the life-giving power of Christ. Still others have a genuine faith in Christ but it is only visible once a week during church services. This is why we should be very careful to preach the gospel in its entirety. Jesus offers full and free salvation, but he also commands obedience and sacrificial service. Forgiveness from sin is received by turning from our sin and putting our trust in Christ alone for our salvation. Repentance and faith are two sides of the same coin, and both must be present before people can actively participate in the life of the church.
Belonging to Christ must also be expressed in some clear and practical ways. In the New Testament church two things immediately happened as new believers began their new life in Christ - they were baptised in water and they received the gift of the Holy Spirit. In this way new believers became firmly established and were ready to follow Christ, fully equipped for a life of discipleship and witness.
All these elements are necessary in order to make a good beginning in your life in Christ and to become a useful member of the body of Christ - repenting from sin, believing in Christ, being baptized in water and in the Holy Spirit. Then you are ready to take up your place in the body of Christ to serve God and to be a blessing to his people.