Ambrose of Milan, on Titus 1:6

I have set down these things which I have been told are to be avoided, but the Apostle is the Master of virtues, and he teaches that gainsayers are to be convicted with patience, who lays down that one should be the husband of a single wife, not in order to exclude him from the right of marriage (for this is beyond the force of the precept), but that by conjugal chastity he may preserve the grace of his baptismal washing; nor again that he may be induced by the Apostle's authority to beget children in the priesthood; for the speaks of having children, not of begetting them, or marrying again.

And I have thought it well not to pass by this point, because many contend that having one wife is said of the time after Baptism; so that the fault whereby any obstacle would ensue would be washed away in baptism. And indeed all faults and sins are washed away; so that if anyone have polluted his body with very many whom he has bound to himself by no law of marriage, all the sins are forgiven him, but if any one have contracted a second marriage it is not done away; for sin not law is loosed by the laver, and as to baptism there is no sin but law. That then which has to do with law is not remitted as though it were sin, but is retained. And the Apostle has established a law, saying: "If any man be without reproach the husband of one wife." So then he who is without blame the husband of one wife comes within the rule for undertaking the priestly office; he, however, who has married again has no guilt of pollution, but is disqualified for the priestly prerogative.