"It may be asked: “Why ought they to have mourned over another man’s sin?” I answer, for two reasons: first, in consequence of the communion that exists among the members of the Church, it was becoming that all should feel hurt at so deadly a fall on the part of one of their number; and secondly, when such an enormity is perpetrated in a particular Church, the perpetrator of it is all offender in such a way, that the whole society is in a manner polluted. For as God humbles the father of a family in the disgrace of his wife, or of his children, and a whole kindred in the disgrace of one of their number, so every Church ought to consider, that it contracts a stain of disgrace whenever any base crime is perpetrated in it. Nay, farther, we see how the anger of God was kindled against the whole nation of Israel on account of the sacrilege of one individual — Achan. (Joshua 7:1.) It was not as though God had been so cruel as to take vengeance on the innocent for another man’s crime; but, as in every instance in which anything of this nature has occurred among a people, there is already some token of his anger, so by correcting a community for the fault of one individual, he distinctly intimates that the whole body is infected and polluted with the contagion of the offense. Hence we readily infer, that it is the duty of every Church to mourn over the faults of individual members, as domestic calamities belonging to the entire body. And assuredly a pious and dutiful correction takes its rise in our being inflamed with holy zeal through displeasure at the offense; for otherwise severity will be felt to be bitter. 271"
John Calvin, Commentary on I Corinthians 5:1-5