2175 Sunday is expressly distinguished from the sabbath which it follows chronologically every week; for Christians its ceremonial observance replaces that of the sabbath. In Christ’s Passover, Sunday fulfills the spiritual truth of the Jewish sabbath and announces man’s eternal rest in God. For worship under the Law prepared for the mystery of Christ, and what was done there prefigured some aspects of Christ:107
Those who lived according to the old order of things have come to a new hope, no longer keeping the sabbath, but the Lord’s Day, in which our life is blessed by him and by his death.108
2176 The celebration of Sunday observes the moral commandment inscribed by nature in the human heart to render to God an outward, visible, public, and regular worship "as a sign of his universal beneficence to all."109 Sunday worship fulfills the moral command of the Old Covenant, taking up its rhythm and spirit in the weekly celebration of the Creator and Redeemer of his people.
2177 The Sunday celebration of the Lord’s Day and his Eucharist is at the heart of the Church’s life. "Sunday is the day on which the paschal mystery is celebrated in light of the apostolic tradition and is to be observed as the foremost holy day of obligation in the universal Church."110
"Also to be observed are the day of the Nativity of Our Lord Jesus Christ, the Epiphany, the Ascension of Christ, the feast of the Body and Blood of Christi, the feast of Mary the Mother of God, her Immaculate Conception, her Assumption, the feast of Saint Joseph, the feast of the Apostles Saints Peter and Paul, and the feast of All Saints."111
2178 This practice of the Christian assembly dates from the beginnings of the apostolic age.112 The Letter to the Hebrews reminds the faithful "not to neglect to meet together, as is the habit of some, but to encourage one another."113