22 But we must not despair of the conversion of any man, whether situated within or without, so long as "the goodness of God leads him to repentance," and "visits their transgressions with the rod, and their inquiry with stripes." For in this way "He does not utterly take from them His loving-kindness," if they will themselves sometimes "love their own soul, pleasing God." But as the good man "that shall endure unto the end, the same shall be saved," so the bad man, whether within or without, who shall persevere in his wickedness to the end, shall not be saved.
Nor do we say that "all, wheresoever and howsoever baptized, obtain the grace of baptism," if by the grace of baptism is understood the actual salvation which is conferred by the celebration of the sacrament; but many fail to obtain this salvation even within the Church, although it is clear that they possess the sacrament, which is holy in itself. Well, therefore, does the Lord warn us in the gospel that we should not company with ill-advisers, who walk under the pretence of Christ's name; but these are found both within and without, as, in fact, they do not proceed without unless they have first been ill-disposed within.
And we know that the apostle said of the vessels placed in the great house, "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 in what manner each man ought to purge himself from these he shows a little above, saying, "Let every one that names the name of Christ depart from iniquity," that he may not in the last day, with the chaff, whether with that which has already been driven from the threshing-floor, or with that which is to be separated at the last, hear the command, "Depart from me, you that work iniquity." Whence it appears, indeed, as Cyprian says, that "we are not at once to admit and adopt whatsoever is professed in the name of Christ, but only what is done in the truth of Christ." But it is not an action done in the truth of Christ that men should "seize on estates by fraudulent pretenses, and increase their gains by accumulated usury," or that they should "renounce the world in word only;" and yet, that all this is done within the Church, Cyprian himself bears sufficient testimony.
Source: On Baptism, Against the Donatists (New Advent)