Question First. On the Precept of Abstinence

673. On the precept itself. The precept of abstinence, which here is considered separately from the precept of fasting, prohibits three things: a. flesh meat; b. eggs and milk foods; c. the mixture of foods. Furthermore, sometimes only flesh meat is prohibited; sometimes also eggs and milk foods with the mixture of foods are prohibited.

a. Although a canon cannot be adduced by which the precept of abstinence separated from fasting was first prescribed for the universal Church, nevertheless that a precept of this kind exists is certain from various constitutions of the supreme pontiffs, from catechisms, and from the practice of the universal Church.

b. The natural law commands voluntary abstinence from food and drink insofar as the effect to be obtained through fasting is necessary. According to St. Thomas, fasting greatly serves to restrain the desires of the flesh, to make satisfaction for sins, and to raise the mind more freely upward.¹ For fasting is undertaken first to repress the very desire of food and drink, and then all concupiscences of the flesh. But since fasting is more or less necessary for all, for in many things we all offend,² and in all the flesh lusts against the spirit,³ the Church by her laws determines the mode of fasting suitable for all. Nor is this surprising: for a. since our first parents brought ruin into the world by the illicit use of food, abstinence from the licit use of food is an excellent means of sanctifying man and expiating past sins; b. Christ the Lord commended fasting by his own example, when he began the work of redemption with a forty days' fast.

c. Since the Church intends by this precept to repress the concupiscence of the flesh, which is carried toward the delights of food and venery, she especially prohibits those foods which are more savory and nourish the body, and by nourishing the body abundantly excite to luxury. But the flesh of birds and terrestrial animals, and those things which come from them, namely the eggs of birds and the milk of animals, are more savory and nourishing; therefore these especially are prohibited by the Church on days of abstinence.⁴

¹ Summa II-II, q. 147, a. 3.

² Jas. 3.

³ Gal. 5:17.

⁴ Cf. St. Thomas, II-II, q. 147, a. 8.