15 But what attitude do they assume, when it is shown that the holy Cyprian, though he did not himself admit as members of the Church those who had been baptized in heresy or schism, yet held communion with those who did admit them, according to his express declaration, "Judging no one, nor depriving any one of the right of communion if he differ from us?" If he was polluted by communion with persons of this kind, why do they follow his authority in the question of baptism?
But if he was not polluted by communion with them, why do they not follow his example in maintaining unity? Have they anything to urge in their defense except the plea, "We choose to have it so?" What other answer have any sinful or wicked men to the discourse of truth or justice—the voluptuous, for instance, the drunkards, adulterers, and those who are impure in any way, thieves, robbers, murderers, plunderers, evil-doers, idolaters,— what other answer can they make when convicted by the voice of truth, except "I choose to do it;" "It is my pleasure so"?
And if they have in them a tinge of Christianity, they say further, "Who are you that judgest another man's servant?" Yet these have so much more remains of modesty, that when, in accordance with divine and human law, they meet with punishment for their abandoned life and deeds, they do not style themselves martyrs; while the Donatists wish at once to lead a sacrilegious life and enjoy a blameless reputation, to suffer no punishment for their wicked deeds, and to gain a martyr's glory in their just punishment.
As if they were not experiencing the greater mercy and patience of God, in proportion as "executing His judgments upon them little by little, He gives them place of repentance," and ceases not to redouble His scourgings in this life; that, considering what they suffer, and why they suffer it, they may in time grow wise; and that those who have received the baptism of the party of Maximianus in order to preserve the unity of Donatus, may the more readily embrace the baptism of the whole world in order to preserve the peace of Christ; that they may be restored to the root, may be reconciled to the unity of the Church, may see that they have nothing left for them to say, though something yet remains for them to do; that for their former deeds the sacrifice of loving-kindness may be offered to a long-suffering God, whose unity they have broken by their wicked sin, on whose sacraments they have inflicted such a lasting wrong.
For "the Lord is merciful and gracious, slow to anger, plenteous in mercy and truth." Let them embrace His mercy and long-suffering in this life, and fear His truth in the next. For He wills not the death of a sinner, but rather that he should turn from his way and live; because He bends His judgment against the wrongs that have been inflicted on Him. This is our exhortation.
Source: On Baptism, Against the Donatists (New Advent)