Chapter I: Sunday and Its Observance
8. "By a tradition handed down from the apostles and having its origin from the very day of Christ's resurrection, the Church celebrates the paschal mystery every eighth day, which, with good reason, bears the name of the Lord's Day or Sunday." 
9. Evidence of the gathering of the faithful on the day which the New Testament itself already designates as the Lord's Day  appears explicitly in documents of the first and second centuries.  Outstanding among such evidence is the testimony of Saint Justin: "On this day which is called Sunday, all who live in the cities or in the country gather together in one place."  But the day of gathering for Christians did not coincide with the day of rest in the Greek or Roman calendar and therefore event he gathering on this day was a sign to fellow citizens of the Christians' identity.
10. From the earliest centuries pastors had never failed to counsel their people on the need to gather together on Sunday. " Because you are Christ's members, do not scatter from the church by not coming together . . . do not neglect your Savior or separate him from his members. Do not shatter or scatter the Body of Christ . . . ."  Vatican Council II recalled this teaching in the following words: "On this day Christ's faithful must gather together, so that, by hearing the word of God and taking part in the eucharist, they may call to mind the passion, resurrection, and glorification of the Lord Jesus and may thank God, who 'has begotten them again unto a living hope through the resurrection of Jesus Christ from the dead' " (1 Peter 1:3). 
11. Saint Ignatius of Antioch pointed out the importance of the Sunday celebration for the life of the faithful: "Christians no longer observe the sabbath day, but live according to the Lord's Day, on which our life was restored through Jesus Christ and his death."  In their " sense of the faith" (sensus fidelium) the faithful, now as in the past, have held the Lord's Day in such high regard that they have never willingly omitted its observance even in times of persecution or in the midst of cultures alien or hostile to the Christian faith.
12. The following are the principal requisites for the Sunday assembly of the faithful.
- the gathering of the faithful to manifest the Church, not simply on their own initiative but as called together by God, that is, as the people of God in their organic structure, presided over by a priest, who acts in the person of Christ;
- their instruction in the paschal mystery through the Scriptures that are proclaimed and that are explained by a priest or deacon;
- the celebration of the eucharistic sacrifice, by which the paschal mystery is expressed, and which is carried out by the priest in the person of Christ and offered in the name of the entire Christian people.
13. Pastoral efforts should have this aim above all that the sacrifice of the Mass on Sunday be regarded as the only true actualization of the Lord's paschal mystery  and as the most complete manifestation of the Church: "Hence the Lord's Day is the first holyday of all and should be proposed to the devotion of the faithful and taught to them. . . . Other celebrations, unless they be truly of great importance, shall not have precedence over the Sunday, the foundation and core of the whole liturgical year." 
14. Such principles should be set before the faithful and instilled in them right from the beginning of their Christian formation, in order that they may willingly fulfill the precept to keep this day holy and may understand why they are brought together for the celebration of the eucharist by the call of the Church  and not simply by their personal devotion. In this way the faithful will be led to experience the Lord's Day as a sign of the divine transcendence over all human works, and not simply a day off from work; in virtue of the Sunday assembly they will more deeply perceive themselves to be members of the Church and will show this outwardly.
15. In the Sunday assembly, as also in the life of the Christian community, the faithful should find both active participation and a true spirit of community, as well as the opportunity to be renewed spiritually under the guidance of the Holy Spirit. In this way, too, they will be protected against the attractions of sects that promise relief from the pain of loneliness and a more complete fulfillment of religious aspirations.
16. Finally, pastoral effort should concentrate on measures which have as their purpose "that the Lord's Day becomes in fact a day of joy and of freedom from work."  In this way Sunday will stand out in today's culture as a sign of freedom and consequently as a day established for the well-being of the human person, which clearly is a higher value than commerce or industrial production. 
17. The word of God, the eucharist, and the ministry of the priest are gifts that the Lord presents to the Church, his Bride, and they are to be received and to be prayed for as divine graces. The Church, which possesses these gifts above all in the Sunday assembly, thanks God for them in that same assembly and awaits the joy of complete rest in the day of the Lord "before the throne of God and before the Lamb."