14 But if the baptism of heretics can have the regeneration of the second birth, those who are baptized among them must be counted not heretics, but children of God. For the second birth, which occurs in baptism, begets sons of God. But if the spouse of Christ is one, which is the Catholic Church, it is she herself who alone bears sons of God. For there are not many spouses of Christ, since the apostle says, “I have espoused you, that I may present you as a chaste virgin to Christ;” and, “Hearken, O daughter, and consider, and incline your ear; forget also your own people, for the King has greatly desired your beauty;” and, Come with me, my spouse, from Lebanon; you shall come, and shall pass over from the source of your faith; and, “I have come into my garden, my sister, my spouse.” We see that one person is everywhere set forward, because also the spouse is one.
But the synagogue of heretics is not one with us, because the spouse is not an adulteress and a harlot. Whence also she cannot bear children of God; unless, as appears to Stephen, heresy indeed brings them forth and exposes them, while the Church takes them up when exposed, and nourishes those for her own whom she has not born, although she cannot be the mother of strange children. And therefore Christ our Lord, setting forth that His spouse is one, and declaring the sacrament of His unity, says, “He that is not with me is against me, and he that gathers not with me scatters.” For if Christ is with us, but the heretics are not with us, certainly the heretics are in opposition to Christ; and if we gather with Christ, but the heretics do not gather with us, doubtless they scatter.
Source: The Epistles of Cyprian (New Advent)