“Is church membership important?”
The words “member” and “members” occur many times in the New Testament. Conceptually, church membership is a product of metaphor. The various parts of a human body — feet, hands, eyes, ears, etc. — constitute its members. In the same way, all who believe in the Lord Jesus Christ are members of the church, which the Bible refers to as a spiritual body.
Is that important? Absolutely. But we should be clear what that means and does not mean, since Christians often use the word “membership” in ways the Bible does not.