10 Such are the conditions, son Oceanus, which the master-teachers of the church ought with anxiety and fear to require of others and to observe themselves. Such too are the canons which they should follow in the choice of persons for the priesthood; for they must not interpret the law of Christ to suit private animosities and feuds or to gratify ill-feeling which is sure to recoil on the man who cherishes it. Consider how unimpeachable is the character of Carterius in whose life his ill-wishers can find nothing to censure except a marriage contracted before baptism. “He that said, Do not commit adultery, said also, Do not kill. If we commit no adultery yet if we kill, we have become transgressors of the law.” “Whosoever shall keep the whole law and yet offend in one point, he is guilty of all.” Accordingly when they cast in our teeth a marriage entered into before baptism, we must require of them compliance with all the precepts which are given to the baptized. For they pass over much that is not allowable while they censure much that is allowed.
Source: Letters (New Advent)