Question: "Why is church membership important?"
Answer: The universal Church—the Body of Christ (Romans 12:5)—is composed of all true believers in Christ, but there is nothing in the Bible about “membership” in a local church assembly. As believers, we have our names written in the Lamb’s book of life (Revelation 20:12), which is the only “membership roll” spoken of in Scripture.
The New Testament churches apparently had no need of formal membership, relying instead on God to gather together believers in a local body. “And the Lord added to them day by day those that were being saved” (Acts 2:47). This verse indicates that salvation was a prerequisite for being “added” to the church. Churches today who require salvation before membership are simply following the biblical model. See also 2 Corinthians 6:14-18.
Although there is no scriptural mandate for church membership, there is certainly nothing to prohibit it. Church membership is a way of officially identifying oneself with a local body of believers. Church membership is a statement that a Christian is in agreement with that local church and is willing to be identified as a representative of it. Church membership is also valuable for organizational purposes and a good way of determining who is allowed to vote on important church decisions and/or who is involved in official church positions and functions. Church membership is not required of Christians. It is simply a way of saying, "I am a Christian and I believe _____ church is a good church."