CATECHISM OF THE CATHOLIC CHURCH
SECOND EDITION

Paragraphs 1162–1166

1162 "The beauty of the images moves me to contemplation, as a meadow delights the eyes and subtly infuses the soul with the glory of God." Similarly, the contemplation of sacred icons, united with meditation on the Word of God and the singing of liturgical hymns, enters into the harmony of the signs of celebration so that the mystery celebrated is imprinted in the heart's memory and is then expressed in the new life of the faithful.
1163 "Holy Mother Church believes that she should celebrate the saving work of her divine Spouse in a sacred commemoration on certain days throughout the course of the year. Once each week, on the day which she has called the Lord's Day, she keeps the memory of the Lord's resurrection. She also celebrates it once every year, together with his blessed Passion, at Easter, that most solemn of all feasts. In the course of the year, moreover, she unfolds the whole mystery of Christ. . . . Thus recalling the mysteries of the redemption, she opens up to the faithful the riches of her Lord's powers and merits, so that these are in some way made present in every age; the faithful lay hold of them and are filled with saving grace."
1164 From the time of the Mosaic law, the People of God have observed fixed feasts, beginning with Passover, to commemorate the astonishing actions of the Savior God, to give him thanks for them, to perpetuate their remembrance, and to teach new generations to conform their conduct to them. In the age of the Church, between the Passover of Christ already accomplished once for all, and its consummation in the kingdom of God, the liturgy celebrated on fixed days bears the imprint of the newness of the mystery of Christ.
1165 When the Church celebrates the mystery of Christ, there is a word that marks her prayer: "Today!" - a word echoing the prayer her Lord taught her and the call of the Holy Spirit. This "today" of the living God which man is called to enter is "the hour" of Jesus' Passover, which reaches across and underlies all history:

Life extends over all beings and fills them with unlimited light; the Orient of orients pervades the universe, and he who was "before the daystar" and before the heavenly bodies, immortal and vast, the great Christ, shines over all beings more brightly than the sun. Therefore a day of long, eternal light is ushered in for us who believe in him, a day which is never blotted out: the mystical Passover.

1166 "By a tradition handed down from the apostles which took its origin from the very day of Christ's Resurrection, the Church celebrates the Paschal mystery every seventh day, which day is appropriately called the Lord's Day or Sunday." The day of Christ's Resurrection is both the first day of the week, the memorial of the first day of creation, and the "eighth day," on which Christ after his "rest" on the great sabbath inaugurates the "day that the Lord has made," the "day that knows no evening." The Lord's Supper is its center, for there the whole community of the faithful encounters the risen Lord who invites them to his banquet:

The Lord's day, the day of Resurrection, the day of Christians, is our day. It is called the Lord's day because on it the Lord rose victorious to the Father. If pagans call it the "day of the sun," we willingly agree, for today the light of the world is raised, today is revealed the sun of justice with healing in his rays.