“We believe also in the holy Church, that is, the Catholic Church. For heretics violate the faith itself by a false opinion about God; schismatics, however, withdraw from fraternal love by hostile separations, although they believe the same things we do. Consequently, neither heretics nor schismatics belong to the Catholic Church; not heretics, because the Church loves God; and not schismatics, because the Church loves neighbor” (Faith and the Creed 10:21 [A.D. 393]).
“[J]ust as baptism is of no profit to the man who renounces the world in words and not in deeds, so it is of no profit to him who is baptized in heresy or schism; but each of them, when he amends his ways, begins to receive profit from that which before was not profitable, but was yet already in him” (On Baptism, Against the Donatists 4:4 [A.D. 400]).
“I do not hesitate to put the Catholic catechumen, burning with divine love, before a baptized heretic. Even within the Catholic Church herself we put the good catechumen ahead of the wicked baptized person . . . For Cornelius, even before his baptism, was filled up with the Holy Spirit [Acts 10:44–48], while Simon [Magus], even after his baptism, was puffed up with an unclean spirit [Acts 8:13–19]” (ibid., 4:21).
“The apostle Paul said, ‘As for a man that is a heretic, after admonishing him once or twice, have nothing more to do with him’ [Titus 3:10]. But those who maintain their own opinion, however false and perverted, without obstinate ill will, especially those who have not originated the error of bold presumption, but have received it from parents who had been led astray and had lapsed . . . those who seek the truth with careful industry and are ready to be corrected when they have found it, are not to be rated among heretics” (Letters 43:1 [A.D. 412]).
“Whoever is separated from this Catholic Church, by this single sin of being separated from the unity of Christ, no matter how estimable a life he may imagine he is living, shall not have life, but the wrath of God rests upon him” (ibid., 141:5).