Biblical baptism serves as a declaration of our participation in the body of Christ, the church. Biblical baptism is also an act of submission. When we are baptized we are humbly admitting that we are sinners who can't forgive our own sins. We admit we need Jesus Christ as Savior.
The term "church membership" is not a Bible term. However, the concept definitely is biblical! Church membership is the mutual acceptance and commitment of the church body to the individual and the individual to the church body.