Chapter 19.
25 They indeed who say that baptism is not to be repeated, because only hands were laid on those whom Philip the deacon had baptized, are saying what is quite beside the point; and far be it from us, in seeking the truth, to use such arguments as this. Wherefore we are all the further from "yielding to heretics," if we deny that what they possess of Christ's Church is their own property, and do not refuse to acknowledge the standard of our General because of the crimes of deserters; nay, all the more because "the Lord our God is a jealous God," let us refuse, whenever we see anything of His with an alien, to allow him to consider it his own. For of a truth the jealous God Himself rebukes the woman who commits fornication against Him, as the type of an erring people, and says that she gave to her lovers what belonged to Him, and again received from them what was not theirs but His. In the hands of the adulterous woman and the adulterous lovers, God in His wrath, as a jealous God, recognizes His gifts; and do we say that baptism, consecrated in the words of the gospel, belongs to heretics? And are we willing, from consideration of their deeds, to attribute to them even what belongs to God, as though they had the power to pollute it, or as though they could make what is God's to be their own, because they themselves have refused to belong to God?
26. Who is that adulterous woman whom the prophet Hosea points out, who said, "I will go after my lovers, that give me my bread and my water, my wool and my flax, and everything that befits me?" Let us grant that we may understand this also of the people of the Jews that went astray; yet whom else are the false Christians (such as are all heretics and schismatics) wont to imitate, except false Israelites? For there were also true Israelites, as the Lord Himself bears witness to Nathanael, "Behold an Israelite indeed, in whom is no guile." But who are true Christians, save those of whom the same Lord said, "He that has my commandments, and keeps them, he it is that loves me?" But what is it to keep His commandments, except to abide in love? Whence also He says, "A new commandment I give unto you, that you love one another;" and again, "By this shall all men know that you are my disciples, if you have love one to another." But who can doubt that this was spoken not only to those who heard His words with their fleshly ears when He was present with them, but also to those who learn His words through the gospel, when He is sitting on His throne in heaven? For He came not to destroy the law, but to fulfill. But the fulfilling of the law is love. And in this Cyprian abounded greatly, insomuch that though he held a different view concerning baptism, he yet did not forsake the unity of the Church, and was in the Lord's vine a branch firmly rooted, bearing fruit, which the heavenly Husbandman purged with the knife of suffering, that it should bear more fruit. But the enemies of this brotherly love, whether they are openly without, or appear to be within, are false Christians, and antichrists. For when they have found an opportunity, they go out, as it is written: "A man wishing to separate himself from his friends, seeks opportunities." But even if occasions are wanting, while they seem to be within, they are severed from that invisible bond of love. Whence St. John says, "They went out from us, but they were not of us; for had they been of us, they would no doubt have continued with us." He does not say that they ceased to be of us by going out, but that they went out because they were not of us. The Apostle Paul also speaks of certain men who had erred concerning the truth, and were overthrowing the faith of some; whose word was eating as a canker. Yet in saying that they should be avoided, he nevertheless intimates that they were all in one great house, but as vessels to dishonor—I suppose because they had not as yet gone out. Or if they had already gone out, how can he say that they were in the same great house with the honorable vessels, unless it was in virtue of the sacraments themselves, which even in the severed meetings of heretics are not changed, that he speaks of all as belonging to the same great house, though in different degrees of esteem, some to honor and some to dishonor? For thus he speaks in his Epistle to Timothy: "But shun profane and vain babblings; for they will increase unto more ungodliness. And their word will eat as does a canker; of whom is Hymenæus and Philetus; who concerning the truth have erred, saying that the resurrection is past already; and overthrow the faith of some. Nevertheless the foundation of God stands firm, having this seal, The Lord knows them that are His. And, Let every one that names the name of Christ depart from iniquity. But in a great house there are not only vessels of gold and of silver, but also of wood and of earth; and some to honor, and some to dishonor. If a man therefore purge himself from these, he shall be a vessel unto honor, sanctified, and meet for the master's use, and prepared unto every good work." But what is it to purge oneself from such as these, except what he said just before, "Let every one that names the name of Christ depart from iniquity." And lest any one should think that, as being in one great house with them, he might perish with such as these, he has most carefully forewarned them, "The Lord knows them that are His,"— those, namely, who, by departing from iniquity, purge themselves from the vessels made to dishonor, lest they should perish with them whom they are compelled to tolerate in the great house.
Source: On Baptism, Against the Donatists (New Advent)