Many people have truly come to know Christ as Savior after having been sincere, religious “church members” for years. Though faithful supporters of some earthly church organization they had never experienced the truth of II Cor. 5:17: “If any man be in Christ he is a new creation.” It is possible to be a member in good standing of some church organization, yet be outside of the one true Church of which the Bible speaks.
This is because the true Bible Church is not an organization but a living organism, a spiritual body, with a living Head and living members. Again and again St. Paul, by divine inspiration, calls the Church, the Body of Christ. He says: “We being many, are one Body in Christ…” (Rom. 12:5). “Ye are the Body of Christ, and members in particular” (I Cor. 12:27). “We are members of His Body” (Eph. 5:30).
How do we become members of this true Bible Church, the Body of Christ? First, we must acknowledge ourselves to be sinners in God’s sight, for Ephesians 2 relates how Christ died for sinful men that He might “reconcile” them to God “in one Body” by the cross (Eph. 2:16). Thus, when believing sinners are reconciled to God by faith in Christ, they are regenerated, given a new life, by the Spirit, and by the Spirit are baptized into the Church, the Body of Christ. source