If you take your cues from the contemporary evangelical world, it's a voluntary society - like the Kiwanis or Rotary club, like the Gideons or YMCA. Apparently we've learned our ecclessiology from John Locke. Locke wrote,
"A church, then, I take to be a voluntary society of men, joining themselves together of their own accord in order to the public worshipping of God in such manner as they judge acceptable to Him, and effectual to the salvation of their souls. I say it is a free and voluntary society. Nobody is born a member of any church; ...everyone joins himself voluntarily to that society in which he believes he has found that profession and worship which is truly acceptable to God. The hope of salvation, as it was the only cause of his entrance into that communion, so it can be the only reason of his stay there. For if afterwards he discover anything either erroneous in the doctrine or incongruous in the worship of that society to which he has joined himself, why should it not be as free for him to go out as it was to enter? A church, then, is a society of members voluntarily uniting to that end" (emphasis added).That's different than another John I know. Calvin wrote,
"When we say that the pure ministry of the word and pure celebration of the sacraments is a fit pledge and earnest, so that we may safely recognize a church in every society in which both exist, our meaning is, that we are never to discard it so long as these remain, though it may otherwise teen with numerous faults. Nay, even in the administration of word and sacraments defects may creep in which ought not to alienate us from its communion...we are not on account of every minute difference to abandon a church, provided it retain sound and unimpaired that doctrine in which the safety of piety consists, and keep the use of the sacraments instituted by the Lord" (Institutes, 4.1.11).Calvin has spoken. It's not a voluntary association to be thrown away lightly on account of any little disagreement. But what does Scripture say? What is the church?
It is not a simple question, or not a question that one can answer simply. The Bible piles up the metaphors to describe the church: body, building, bride, temple, family, etc. Sometimes the Scriptures seem to speak of the church in its ideal state, other times in the very real, impure state we experience it in now. The distinction between the invisible church and the visible church is incredibly important and helpful when held together.
Calvin acknowledges both aspects, writing, "I have observed that the Scriptures speak of the church in two ways. Sometimes when they speak of the the Church they mean the Church as it really is before God - the Church into which none are admitted but those who by the gift of adoption are sons of God, and by the sanctification of the Spirit true members of Christ"
In this case, the church is comprised of all the elect scattered across the globe and all the saints who have ever lived. This is the invisible church. But Calvin recognizes the visible church and it's indispensability too,
"Often, too, by the name of Church is designated the whole body of mankind scattered throughout the world, who profess to worship one God and Christ, who by baptism are initiated into the faith; by partaking of the Lord's Supper profess unity in true doctrine and charity, agree in holding the word of the Lord and observe the ministry which Christ has appointed for the preaching of it"
Before jumping all over the part about baptism, notice the very visible nature of it. This isn't a subjective thing, but very objective. Do you confess the faith of the Church? Have you been baptized? Do you partake? Do you go to church? Then you are a part of the church.
Calvin could be mistakenly taken to mean here that the church is the simply the collection of individual believers. It is that, but it's more - it's the Mother and her children, the institution and the members of it. He speaks of the Church "into whose bosom God is pleased to collect his children, not only that by her aid and ministry they may be nourished so long as they are babes and children, but also be guided by her maternal care until they grow up into manhood, and finally attain to the perfection of faith"
Interestingly, Calvin felt he needed to qualify his statement, saying that when he speaks of the church, he doesn't JUST mean the visible church, but all the elect. Today, I think he'd qualify in the opposite way - I don't JUST mean the invisible church.
Again, the emphasis is on the objective, not our subjective evaluation of our (or someone else's) faith. When speaking of the invisible church, it's based on the objective decree of God in election. When speaking of the visible church, it's based on the objective confession, baptism, and participation in the church.
Well, long post and not a single verse of Scripture. We shall have to remedy that next post.