The first day of the week, also called the “Lord’s Day,” is set aside for public worship. This was true in the early Church under the Apostles who recognized that the Christian mystery supplanted that of the Old Law, the Sabbath.
On this day, called Dominica in Latin, Catholics are obliged by law to assist at the Sacrifice of the Mass. The faithful may satisfy the Sunday precept of attending the celebration of the Eucharist by participating in the Mass in the evening of the preceding Saturday. This same grant extends to the time before a holy day of obligation.
Liturgically, Sunday was focused on the celebration of the Eucharist, noted as requisite on this “first day of creation,” or on this “eighth day,” one day added to the seven-day week to signify perfection. One entered into the kingdom of God through the Eucharist on Sunday, a day both in and out of time, to experience what will be realized fully only in the kingdom.
The General Norms for the Liturgical Year state that “the Church celebrates the paschal mystery on the first day of the week, known as the Lord’s Day [and that] Sunday must be ranked as the first holy day of all. Because of its special importance, the Sunday celebration gives way only to solemnities or feasts of the Lord.”
The faithful are bound to participate in the Mass and are to abstain from those labors and business concerns which impede worship to be rendered to God, and the proper relaxation of mind and body. This is a grave obligation, and willful neglect of it can constitute a serious sin. (6:31)