Church membership is not about signing a contract or joining a club.
It is one thing to attend church, it is quite another thing to become a participating member of a local church. While the term ‘church member’ never occurs in the Bible, it is clear that Christians were committed to each other in local communities.
Christians met together for teaching, caring, sharing communion, mission and prayer. When Paul wrote letters it is clear there are local congregations of believers committed to each other because they are committed to God, and they met regularly together.
Acts 13:1-3 1 Corinthians 16:2, 19