I had pretty much taken it for granted that believers understood the importance of church membership, until recently a man visiting our church told me that he didn’t believe in church membership. Below are a couple of reasons for church membership that I have taken from John Piper’s website, www.desiringgod.org:
Church Government Implies a Membership of Accountability
The New Testament teaches that the local church has elders or overseers who have special responsibility to equip (Ephesians 4:11) and care for (Acts 20:28) and teach (1 Timothy 3:2; Titus 1:9) the members. The New Testament teaches that the members are to respect (1 Thessalonians 5:12f.) and be submissive to (Hebrews 13:17) these leaders, but not to treat them as infallible (1 Timothy 5:20) or in the place of Christ (Matthew 23:8-12). They are servants, not masters (Luke 22:26), and their leadership comes from their divine call to serve (Acts 20:28), not from their desire to rule. Their leadership does not replace the congregation of believers as the body with final authority under the Lord (Matthew 18:17; 1 Corinthians 5:4; Acts 6:3; 15:22).
Leadership and submission have no meaning where there is no commitment to accountability (that is, to membership).
Church Discipline Implies a Membership of Accountability
Jesus said, “If your brother sins against you, go and tell him his fault, between you and him alone. If he listens to you, you have gained your brother. But if he does not listen, take one or two others along with you, that every word may be confirmed by the evidence of two or three witnesses. If he refuses to listen to them, tell it to the church; and if he refuses to listen even to the church, let him be to you as a Gentile and a tax collector” (Matthew 18:15-17).
What this implies is that Christians are to be members of churches where they are held accountable to walk in a way that pleases the Lord. If there were no relationship of accountability, it would be meaningless to “tell it to the church,” because the offending person would simply say, “That church has no jurisdiction over me.”
In summary, church membership holds us accountable to the covenant of faith into which we have entered.