What, after all, is church membership? I would argue that it is a covenant grounded in the affirmations of both the church through the elders, and the member. That is, the member publicly affirms both his dependence on the finished work of Christ alone, his affirmation of the faith once delivered, and his willingness to submit to the church. The church, on the other hand, affirms its conviction, through the elders of the credibility of the profession of faith of the member, and vows to serve and protect the member through the means of grace, including faithful church discipline. To put it more simply, the undershepherds affirm the sheepness of the member, the member the undershepherdness of the elders.
R.C. Sproul Jr.