Further, holiness of life is required in one who receives an order, that he may be qualified to exercise it. Now a man sins mortally if he present himself for orders in mortal sin. Much more therefore does he sin mortally whenever he exercises his order.
I answer that, The law prescribes ( Dt. 16:20 ) that "man should follow justly after that which is just." Wherefore whoever fulfills unworthily the duties of his order follows unjustly after that which is just, and acts contrary to a precept of the law, and thereby sins mortally. Now anyone who exercises a sacred office in mortal sin, without doubt does so unworthily. Hence it is clear that he sins mortally.
Reply to Objection 1: He is not perplexed as though he were in the necessity of sinning; for he can renounce his sin, or resign his office whereby he was bound to the exercise of his order.
Reply to Objection 2: The natural law allows of no dispensation; and it is of natural law that man handle holy things holily. Therefore no one can dispense from this.
Reply to Objection 3: So long as a minister of the Church who is in mortal sin is recognized by the Church, his subject must receive the sacraments from him, since this is the purpose for which he is bound to him. Nevertheless, outside the case of necessity, it would not be safe to induce him to an execution of his Order, as long as he is conscious of being in mortal sin, which conscience, however, he can lay aside since a man is repaired in an instant by Divine grace.
Reply to Objection 4: When any man performs an action as a minister of the Church while in a state of mortal sin, he sins mortally, and as often as he performs that action, since, as Dionysius says (Eccl. Hier. i), "it is wrong for the unclean even to touch the symbols," i.e. the sacramental signs. Hence when they touch sacred things in the exercise of their office they sin mortally. It would be otherwise if they were to touch some sacred thing or perform some sacred duty in a case of necessity, when it would be allowable even to a layman, for instance if they were to baptize in a case of urgency, or gather up the Lord's body should it be cast to the ground.