“Church ‘membership’ is not addressed in the Bible. In the times the Bible was written, there was typically one church per region, as opposed to dozens today. Back then, the shepherds (elders and ministers) knew who was a Christian and who wasn’t, and who was under their care. When you place membership today you are putting yourself under the shepherd’s care, identifying as a brother or sister in Christ, and committing yourself serving Christ with an established group of believers. Membership gives you a voice in church matters as voting ministers and budgets.
Any immersed believer in Christ who is living for Him is welcome to place membership. We ask before you do so to speak to with an elder or minister. This would allow us to answer your questions and explain the responsibilities every Christian should have in His Church.
Article on Church Membership
LeRoy Lawson's book: The Family of God (The Meaning of Church Membership)