Summa Theologica Suppl, q. 64: Of the Things Annexed to Marriage, and First of the Payment of the Marriage Debt
Article 7. Whether it is forbidden to demand the debt on holy days?
Objection 1It would seem that a person ought not to be forbidden to ask for the debt on holy days. For the remedy should be applied when the disease gains strength. Now concupiscence may possibly gain strength on a feast day. Therefore the remedy should be applied then by asking for the debt.
Objection 2Further, the only reason why the debt should not be demanded on feast days is because they are devoted to prayer. Yet on those days certain hours are appointed for prayer. Therefore one may ask for the debt at some other time.
On the contraryJust as certain places are holy because they are devoted to holy things, so are certain times holy for the same reason. But it is not lawful to demand the debt in a holy place. Therefore neither is it lawful at a holy time.
I answer thatAlthough the marriage act is void of sin, nevertheless since it oppresses the reason on account of the carnal pleasure, it renders man unfit for spiritual things. Therefore, on those days when one ought especially to give one's time to spiritual things, it is not lawful to ask for the debt.
Reply to Objection 1At such a time other means may be employed for the repression of concupiscence; for instance, prayer and many similar things, to which even those who observe perpetual continence have recourse.
Reply to Objection 2Although one is not bound to pray at all hours, one is bound throughout the day to keep oneself fit for prayer.
Article 8. Whether it is a mortal sin to ask for the debt at a holy time?
Objection 1It would seem that it is a mortal sin to ask for the debt at a holy time. For Gregory says (Dial. i) that the devil took possession of a woman who had intercourse with her husband at night and came in the morning to the procession. But this would not have happened had she not sinned mortally. Therefore, etc.
Objection 2Further, whoever disobeys a Divine command commits a mortal sin. Now the Lord commanded (Ex. 19:15): "Come not near your wives," when namely they were about to receive the Law. Much more therefore do husbands sin mortally if they have intercourse with their wives at a time when they should be intent on the sacred observances of the New Law.
On the contraryNo circumstance aggravates infinitely. But undue time is a circumstance. Therefore it does not aggravate a sin infinitely, so as to make mortal what was otherwise venial.
I answer thatTo ask for the debt on a feast day is not a circumstance drawing a sin into another species; wherefore it cannot aggravate infinitely. Consequently a wife or husband does not sin mortally by asking for the debt on a feast day. It is however a more grievous sin to ask for the sake of mere pleasure, than through fear of the weakness of the flesh.
Reply to Objection 1This woman was punished not because she paid the debt, but because afterwards she rashly intruded into the divine service against her conscience.
Reply to Objection 2The authority quoted shows not that it is a mortal sin but that it is unbecoming. For under the Old Law which was given to a carnal people many things were required under an obligation of precept, for the sake of bodily cleanness, which are not required in the New Law which is the law of the spirit.