What is the distinction between the invisible and the visible church? The invisible church, according to Calvin, are those already elected into God's presence (4.1.7). Members of the invisible church are dead, living, and arguably, not yet among us. We worship with the visible church each Lord's Day. The catch is that God knows the difference and we don't. So instead of trying to separate the sheep from the wolves ourselves, we should take care of everyone in front of us so that we might not accidentally harm the sheep (4.1.8). (Calvin does allow later for some corporate sorting [4.1.15], but that shouldn't destroy the main principle.)
What are the marks of the true church? Calvin has only two marks, "Wherever we see the Word of God purely preached and heard, and the sacraments administered according to Christ's institution, there, it is not to be doubted, a church of God exists." (4.1.9) As Lane notes - not discipline, not fellowship (p. 141). If a church promotes Word and Sacrament, it will bear fruit, either now or in the future.
May we ever leave a church to form another church? No. If Calvin tells us once, he tells us a hundred times - stop it! Then follows a list of invalid reasons to leave a church:
* Arguments over non-essential doctrine - Who is supposed to arrange the lilies? Should the worship service extend past 60 minutes?
* Scandal in the church - Is there a divorced person on the Session? Is the Christian Education Director a former felon?
* Members who keep sinning - I saw Steve at the bar again! (Hmm, what were you doing there?)
As I have attempted to show by my own modern examples, I worry that this section of Calvin's teaching might almost be more relevant today than it was in Calvin's time - or at least as relevant. Church leaving and church hopping are all too prevalent. Here are some articles regarding church hopping: some statistics, for, against. What are your thoughts about addressing church hoppers using Calvin and/or the Bible?