On Christmas Day, however, several masses are said on account of Christ's threefold nativity. Of these the first is His eternal birth, which is hidden in our regard, and therefore one mass is sung in the night, in the "Introit" of which we say: "The Lord said unto Me: Thou art My Son, this day have I begotten Thee." The second is His nativity in time, and the spiritual birth, whereby Christ rises "as the day-star in our [Vulg.: 'your'] hearts" (2 Pet. 1:19), and on this account the mass is sung at dawn, and in the "Introit" we say: "The light will shine on us today." The third is Christ's temporal and bodily birth, according as He went forth from the virginal womb, becoming visible to us through being clothed with flesh: and on that account the third mass is sung in broad daylight, in the "Introit" of which we say: "A child is born to us." Nevertheless, on the other hand, it can be said that His eternal generation, of itself, is in the full light, and on this account in the gospel of the third mass mention is made of His eternal birth. But regarding His birth in the body, He was literally born during the night, as a sign that He came to the darknesses of our infirmity; hence also in the midnight mass we say the gospel of Christ's nativity in the flesh.
Likewise on other days upon which many of God's benefits have to be recalled or besought, several masses are celebrated on one day, as for instance, one for the feast, and another for a fast or for the dead.
Reply Obj. 3: As already observed (Q. 73, A. 5), Christ wished to give this sacrament last of all, in order that it might make a deeper impression on the hearts of the disciples; and therefore it was after supper, at the close of day, that He consecrated this sacrament and gave it to His disciples. But we celebrate at the hour when our Lord suffered, i.e. either, as on feast-days, at the hour of Terce, when He was crucified by the tongues of the Jews (Mk. 15:25), and when the Holy Ghost descended upon the disciples (Acts 2:15); or, as when no feast is kept, at the hour of Sext, when He was crucified at the hands of the soldiers (John 19:14), or, as on fasting days, at None, when crying out with a loud voice He gave up the ghost (Matt. 27:46, 50).
Nevertheless the mass can be postponed, especially when Holy orders have to be conferred, and still more on Holy Saturday; both on account of the length of the office, and also because orders belong to the Sunday, as is set forth in the Decretals (dist. 75).
Masses, however, can be celebrated "in the first part of the day," owing to any necessity; as is stated De Consecr., dist. 1.
Reply Obj. 4: As a rule mass ought to be said in the day and not in the night, because Christ is present in this sacrament, Who says (John 9:4, 5): "I must work the works of Him that sent Me, whilst it is day: because the night cometh when no man can work; as long as I am in the world, I am the light of the world." Yet this should be done in such a manner that the beginning of the day is not to be taken from midnight; nor from sunrise, that is, when the substance of the sun appears above the earth; but when the dawn begins to show: because then the sun is said to be risen when the brightness of his beams appears. Accordingly it is written (Mk. 16:1) that "the women came to the tomb, the sun being now risen"; though, as John relates (John 20:1), "while it was yet dark they came to the tomb." It is in this way that Augustine explains this difference (De Consens. Evang. iii).
Exception is made on the night of Christmas eve, when mass is celebrated, because our Lord was born in the night (De Consecr., dist. 1). And in like manner it is celebrated on Holy Saturday towards the beginning of the night, since our Lord rose in the night, that is, "when it was yet dark, before the sun's rising was manifest."
Reply Obj. 5: As is set down in the decree (De Consecr., dist. 1), in virtue of a decree of Pope Alexander II, "it is enough for a priest to celebrate one mass each day, because Christ suffered once and redeemed the whole world; and very happy is he who can worthily celebrate one mass. But there are some who say one mass for the dead, and another of the day, if need be. But I do not deem that those escape condemnation who presume to celebrate several masses daily, either for the sake of money, or to gain flattery from the laity." And Pope Innocent III says (Extra, De Celebr. Miss., chap. Consuluisti) that "except on the day of our Lord's birth, unless necessity urges, it suffices for a priest to celebrate only one mass each day." _______________________
THIRD ARTICLE [III, Q. 83, Art. 3]
Whether This Sacrament Ought to Be Celebrated in a House and with
Sacred Vessels?