schism · 311 · Carthage
When the Great Persecution ended, the African church had to decide what to do about the traditores — clergy who had handed over the scriptures to be burned. In 311 a bishop of Carthage was consecrated by a man believed to have been one, and a rival was elected against him; Donatus succeeded that rival and gave the movement its name and its cast of mind. The claim is that a sacrament given by an unworthy minister is void, and behind it a whole ecclesiology: the church is the society of the pure, and a man who has failed cannot hand on what he has forfeited. It was not a fringe movement. For most of the fourth century the Donatists were the majority church in Numidia, with their own bishops in every town, and the quarrel ran for three hundred years until the Arab conquest ended both sides together. The answer worked out against them — chiefly by Augustine, who spent decades on it — is that the sacrament belongs to Christ and not to the minister, so that its validity does not depend on his worth. Eusebius preserves the beginning of the imperial involvement: the appeals to Constantine, and the commission of bishops he appointed to hear it, which is the first time an emperor was asked to adjudicate a Christian schism.
Is a sacrament worth anything if the man who gives it betrayed the church?
The Donatists said no. The answer the church gave instead is the reason the question mattered for centuries.