The New Testament uses several metaphors to describe churches... A flock of sheep isn’t a random collection of ewes, rams, and lambs. Shepherds know their flocks. They know which sheep are theirs to care for and which are not. Sheep belong to specific flocks. This is also the way it should be for God’s spiritual sheep. A temple building, just like a church building, shouldn’t have any loose bricks or blocks. If it does, something’s wrong. Each one of them has a definite place. “There is no place,” said an English preacher long ago, “for any loose stone in God’s edifice.” The same analogy is true for a human body. Your body isn’t a casual collection of loosely related parts. You don't keep your fingers in your pocket until you need them. They are joined. They are members of the body. The local body of Christ should be like this also – those joined to Christ, who are members of His body – should express that relationship through a visible membership. And in a household, a family, you’re either a member or you’re not. So if you are part of the family of God, show it by joining a local expression of God’s family.