Reply Obj. 1: The commandments of God are precepts of the natural law, which are, of themselves, necessary for salvation. But the commandments of the Church are about matters which are necessary for salvation, not of themselves, but only through the ordinance of the Church. Hence there may be certain obstacles on account of which certain persons are not bound to keep the fasts in question.
Reply Obj. 2: In children there is a most evident reason for not fasting, both on account of their natural weakness, owing to which they need to take food frequently, and not much at a time, and because they need much nourishment owing to the demands of growth, which results from the residuum of nourishment. Wherefore as long as the stage of growth lasts, which as a rule lasts until they have completed the third period of seven years, they are not bound to keep the Church fasts: and yet it is fitting that even during that time they should exercise themselves in fasting, more or less, in accordance with their age. Nevertheless when some great calamity threatens, even children are commanded to fast, in sign of more severe penance, according to Jonah 3:7, "Let neither men nor beasts . . . taste anything . . . nor drink water."
Reply Obj. 3: Apparently a distinction should be made with regard to pilgrims and working people. For if the pilgrimage or laborious work can be conveniently deferred or lessened without detriment to the bodily health and such external conditions as are necessary for the upkeep of bodily or spiritual life, there is no reason for omitting the fasts of the Church. But if one be under the necessity of starting on the pilgrimage at once, and of making long stages, or of doing much work, either for one's bodily livelihood, or for some need of the spiritual life, and it be impossible at the same time to keep the fasts of the Church, one is not bound to fast: because in ordering fasts the Church would not seem to have intended to prevent other pious and more necessary undertakings. Nevertheless, in such cases one ought seemingly, to seek the superior's dispensation; except perhaps when the above course is recognized by custom, since when superiors are silent they would seem to consent.
Reply Obj. 4: Those poor who can provide themselves with sufficient for one meal are not excused, on account of poverty, from keeping the fasts of the Church. On the other hand, those would seem to be exempt who beg their food piecemeal, since they are unable at any one time to have a sufficiency of food.
Reply Obj. 5: This saying of our Lord may be expounded in three ways. First, according to Chrysostom (Hom. xxx in Matth.), who says that "the disciples, who are called children of the bridegroom, were as yet of a weakly disposition, wherefore they are compared to an old garment." Hence while Christ was with them in body they were to be fostered with kindness rather than drilled with the harshness of fasting. According to this interpretation, it is fitting that dispensations should be granted to the imperfect and to beginners, rather than to the elders and the perfect, according to a gloss on Ps. 130:2, "As a child that is weaned is towards his mother." Secondly, we may say with Jerome [*Bede, Comment. in Luc. v] that our Lord is speaking here of the fasts of the observances of the Old Law. Wherefore our Lord means to say that the apostles were not to be held back by the old observances, since they were to be filled with the newness of grace. Thirdly, according to Augustine (De Consensu Evang. ii, 27), who states that fasting is of two kinds. One pertains to those who are humbled by disquietude, and this is not befitting perfect men, for they are called "children of the bridegroom"; hence when we read in Luke: "The children of the bridegroom cannot fast [*Hom. xiii, in Matth.]," we read in Matt. 9:15: "The children of the bridegroom cannot mourn [*Vulg.: 'Can the children of the bridegroom mourn?']." The other pertains to the mind that rejoices in adhering to spiritual things: and this fasting is befitting the perfect. _______________________
FIFTH ARTICLE [II-II, Q. 147, Art. 5]
Whether the Times for the Church Fast Are Fittingly Ascribed?
Objection 1: It would seem that the times for the Church fast are unfittingly appointed. For we read (Matt. 4) that Christ began to fast immediately after being baptized. Now we ought to imitate Christ, according to 1 Cor. 4:16, "Be ye followers of me, as I also am of Christ." Therefore we ought to fast immediately after the Epiphany when Christ's baptism is celebrated.
Obj. 2: Further, it is unlawful in the New Law to observe the ceremonies of the Old Law. Now it belongs to the solemnities of the Old Law to fast in certain particular months: for it is written (Zech. 8:19): "The fast of the fourth month and the fast of the fifth, and the fast of the seventh, and the fast of the tenth shall be to the house of Judah, joy and gladness and great solemnities." Therefore the fast of certain months, which are called Ember days, are unfittingly kept in the Church.
Obj. 3: Further, according to Augustine (De Consensu Evang. ii, 27), just as there is a fast "of sorrow," so is there a fast "of joy." Now it is most becoming that the faithful should rejoice spiritually in Christ's Resurrection. Therefore during the five weeks which the Church solemnizes on account of Christ's Resurrection, and on Sundays which commemorate the Resurrection, fasts ought to be appointed.