Today’s Catechism sections discuss the Lord’s Day. Supporting material comes from “Sacrosanctum Concilium”.

II. The Lord's Day

This is the day which the LORD has made; let us rejoice and be glad in it.103

The day of the Resurrection: the new creation

2174 Jesus rose from the dead "on the first day of the week."104 Because it is the "first day," the day of Christ's Resurrection recalls the first creation. Because it is the "eighth day" following the sabbath,105 it symbolizes the new creation ushered in by Christ's Resurrection. For Christians it has become the first of all days, the first of all feasts, the Lord's Day (he kuriake hemera, dies dominica) Sunday:

We all gather on the day of the sun, for it is the first day [after the Jewish sabbath, but also the first day] when God, separating matter from darkness, made the world; and on this same day Jesus Christ our Savior rose from the dead.106

Sunday - fulfillment of the sabbath

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.

The Sunday Eucharist

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

Tradition preserves the memory of an ever-timely exhortation: Come to Church early, approach the Lord, and confess your sins, repent in prayer.... Be present at the sacred and divine liturgy, conclude its prayer and do not leave before the dismissal.... We have often said: "This day is given to you for prayer and rest. This is the day that the Lord has made, let us rejoice and be glad in it."114

2179 "A parish is a definite community of the Christian faithful established on a stable basis within a particular church; the pastoral care of the parish is entrusted to a pastor as its own shepherd under the authority of the diocesan bishop."115 It is the place where all the faithful can be gathered together for the Sunday celebration of the Eucharist. The parish initiates the Christian people into the ordinary expression of the liturgical life: it gathers them together in this celebration; it teaches Christ's saving doctrine; it practices the charity of the Lord in good works and brotherly love:

You cannot pray at home as at church, where there is a great multitude, where exclamations are cried out to God as from one great heart, and where there is something more: the union of minds, the accord of souls, the bond of charity, the prayers of the priests.116

IN BRIEF

2190 The sabbath, which represented the completion of the first creation, has been replaced by Sunday which recalls the new creation inaugurated by the Resurrection of Christ.

2191 The Church celebrates the day of Christ's Resurrection on the "eighth day," Sunday, which is rightly called the Lord's Day (cf SC 106).

The Constitution on the Sacred Liturgy, “Sacrosanctum Concilium” discusses the Lord’s Day.

106. 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 eighth day; with good reason this, then, bears the name of the Lord's Day or Sunday. For on this day Christ's faithful are bound to come together into one place so that; by hearing the word of God and taking part in the Eucharist, they may call to mind the passion, the resurrection and the glorification of the Lord Jesus, and may thank God who "has begotten them again, through the resurrection of Jesus Christ from the dead, unto a living hope" (1 Pet. 1:3). Hence the Lord's Day is the original feast day, and it should be proposed to the piety of the faithful and taught to them so that it may become in fact a day of joy and of freedom from work. Other celebrations, unless they be truly of greatest importance, shall not have precedence over the Sunday which is the foundation and kernel of the whole liturgical year.

Footnotes

103 ⇒ Ps 118:24.
104 Cf. ⇒ Mt 28:1; ⇒ Mk 16:2; ⇒ Lk 24:1; ⇒ Jn 20:1.
105 Cf. ⇒ Mk 16:1; ⇒ Mt 28:1.
106 St. Justin, I Apol. 67: PG 6, 429 and 432.
107 Cf. ⇒ 1 Cor 10:11.
108 St. Ignatius of Antioch, Ad Magn. 9, 1: SCh 10, 88.
109 St. Thomas Aquinas, STh II-II 122, 4.
110 ⇒ CIC, can. 1246 # 1.
111 ⇒ CIC, can. 1246 # 2: "The conference of bishops can abolish certain holy days of obligation or transfer them to a Sunday with prior approval of the Apostolic See."
112 Cf. ⇒ Acts 2:42-46; ⇒ 1 Cor 11:17.
113 ⇒ Heb 10:25.
114 Sermo de die dominica 2 et 6: PG 86/1, 416C and 421C.
115 ⇒ CIC, can. 515 # 1.
116 St. John Chrysostom, De incomprehensibili 3, 6: PG 48, 725.