On the Unity of the Catholic Church 10

Hence heresies both have often arisen and still arise, while a perverse mind has no peace, while discordant faithlessness does not hold unity. The Lord permits and allows these things to happen, the choice of one's own freedom remaining, so that, while the test of truth examines our hearts and minds, the unimpaired faith of the approved may shine out in clear light. The Holy Spirit forewarns through the apostle and says: "There must also be heresies, so that those who are approved may be made manifest among you." So the faithful are proved, so the faithless are uncovered; so even before the day of judgment, here too, the souls of the righteous and the unrighteous are already divided and the chaff is separated from the wheat. Hence are those who, of their own accord, set themselves over rash gatherings without divine appointment, who make themselves prelates without any law of ordination, who, though no one gives them the episcopate, take to themselves the name of bishop; whom the Holy Spirit designates in the psalms as sitting in the chair of pestilence, plagues and pestilences of the faith, deceiving with the serpent's mouth and skilled in corrupting truth, vomiting deadly poisons from pestilent tongues, whose speech creeps like a cancer, whose discourse pours a deadly venom into the breasts and hearts of each.