1 Since you were pleased to acquaint us with the letter sent to you by a Donatist presbyter, although, with the spirit of a true Catholic, you regarded it with contempt, nevertheless, to aid you in seeking his welfare if his folly be not incurable, we beg you to forward to him the following reply. He wrote that an angel had enjoined him to declare to you the episcopal succession of the Christianity of your town; to you, forsooth, who hold the Christianity not of your own town only, nor of Africa only, but of the whole world, the Christianity which has been published, and is now published to all nations. This proves that they think it a small matter that they themselves are not ashamed of being cut off, and are taking no measures, while they may, to be engrafted anew; they are not content unless they do their utmost to cut others off, and bring them to share their own fate, as withered branches fit for the flames. Wherefore, even if you had yourself been visited by that angel whom he affirms to have appeared to him—a statement which we regard as a cunning fiction; and if the angel had said to you the very words which he, on the warrant of the alleged command, repeated to you—even in that case it would have been your duty to remember the words of the apostle: “Though we, or an angel from heaven, preach any other gospel unto you than that we have preached unto you, let him be accursed.” For to you it was proclaimed by the voice of the Lord Jesus Christ Himself, that His “gospel shall be preached unto all nations, and then shall the end come.” To you it has moreover been proclaimed by the writings of the prophets and of the apostles, that the promises were given to Abraham and to his seed, which is Christ, when God said unto him: “In your seed shall all nations of the earth be blessed.” Having then such promises, if an angel from heaven were to say to you, “Let go the Christianity of the whole earth, and cling to the faction of Donatus, the episcopal succession of which is set forth in a letter of their bishop in your town,” he ought to be accursed in your estimation; because he would be endeavouring to cut you off from the whole Church, and thrust you into a small party, and make you forfeit your interest in the promises of God.
2. For if the lineal succession of bishops is to be taken into account, with how much more certainty and benefit to the Church do we reckon back till we reach Peter himself, to whom, as bearing in a figure the whole Church, the Lord said: “Upon this rock will I build my Church, and the gates of hell shall not prevail against it!” The successor of Peter was Linus, and his successors in unbroken continuity were these:— Clement, Anacletus, Evaristus, Alexander, Sixtus, Telesphorus, Iginus, Anicetus, Pius, Soter, Eleutherius, Victor, Zephirinus, Calixtus, Urbanus, Pontianus, Antherus, Fabianus, Cornelius, Lucius, Stephanus, Xystus, Dionysius, Felix, Eutychianus, Gaius, Marcellinus, Marcellus, Eusebius, Miltiades, Sylvester, Marcus, Julius, Liberius, Damasus, and Siricius, whose successor is the present Bishop Anastasius. In this order of succession no Donatist bishop is found. But, reversing the natural course of things, the Donatists sent to Rome from Africa an ordained bishop, who, putting himself at the head of a few Africans in the great metropolis, gave some notoriety to the name of “mountain men,” or Cutzupits, by which they were known.
3. Now, even although some traditor had in the course of these centuries, through inadvertence, obtained a place in that order of bishops, reaching from Peter himself to Anastasius, who now occupies that see—this fact would do no harm to the Church and to Christians having no share in the guilt of another; for the Lord, providing against such a case, says, concerning officers in the Church who are wicked: “All whatsoever they bid you observe, that observe and do; but do not ye after their works: for they say, and do not.” Thus the stability of the hope of the faithful is secured, inasmuch as being fixed, not in man, but in the Lord, it never can be swept away by the raging of impious schism; whereas they themselves are swept away who read in the Holy Scriptures the names of churches to which the apostles wrote, and in which they have no bishop. For what could more clearly prove their perversity and their folly, than their saying to their clergy, when they read these letters, “Peace be with you,” at the very time that they are themselves disjoined from the peace of those churches to which the letters were originally written?
Source: Letters (New Advent)