Excommunication

We see the principle in the New Testament of excommunication, where if a person within the church is guilty of gross and heinous sin, and remains impenitent, it is the law of the new covenant that that person be removed from fellowship in church (1 Cor. 5). Not only for their wellbeing, but also for the purity of the church. Such was the case in the Corinthian community when Paul commanded the removal of the incestuous man from the house of God. And yet, at the same time, there is the warning in the New Testament against precipitous action against people in the church because there’s always going to be sin in the church, and always tares growing along with the wheat (Matt. 13). And we are warned not to try to go in there, and just clear out all the tares for fear that we pull out the wheat itself. That's why this kind of action is reserved for gross and heinous crimes by which the whole community is corrupted.

During the Reformation, the sixteenth century, when the church would split asunder, the question that the theologians faced was this, what are the marks of a true church? And in essence, the answer the Reformers gave was this. The three marks of a true church are the gospel is truly preached, the sacraments are duly administered, and the church exercises discipline. This should serve as a reminder to us of how seriously God takes the purity of His church.