Catechism of the Catholic Church
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." 36 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." 37 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: 38
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. 39
1167 Sunday is the pre-eminent day for the liturgical assembly, when the faithful gather "to listen to the word of God and take part in the Eucharist, thus calling to mind the Passion, Resurrection, and glory of the Lord Jesus, and giving thanks to God who 'has begotten them again, by the resurrection of Jesus Christ from the dead' unto a living hope": 40
When we ponder, O Christ, the marvels accomplished on this day, the Sunday of your holy resurrection, we say: "Blessed is Sunday, for on it began creation . . . the world's salvation ... the renewal of the human race .... On Sunday heaven and earth rejoiced and the whole universe was filled with light. Blessed is Sunday, for on it were opened the gates of paradise so that Adam and all the exiles might enter it without fear. 41
English Translation of the Cathechism of the Catholic Church for the United States of America © 1997, United States Catholic Conference, Inc.