Christ loved the church, and he gave his life for it. It is an unselfish decision. Commitment always builds character. Every team must have a roster. Every school must have an enrollment.
Every army has an enlistment.
Even our country takes a census and requires voter registration. Membership identifies our family. The New Testament places a major emphasis on the need for Christians to be accountable to each other for spiritual growth. You cannot be accountable when you're not committed to any specific church family.