Sunday Mass and Holy Day Obligation
It is both a precept of the Church and Church law that Catholics must worship God on Sunday and Holy Days of Obligation by participating in the Holy Mass. This follows from the fact that in the Mass it is Christ Himself who worships the Father, joining our worship to His. In no other way is it possible to adequately give thanks (eucharistia) to God for the blessings of creation, redemption and our sanctification than by uniting our offerings to that of Jesus Christ Himself. Following the example of the Old Covenant the Church does this weekly, on the day of the Lord's Resurrection.
On Sundays and other holy days of obligation the faithful are bound to participate in the Mass; they are also to abstain from those labors and business concerns which impede the worship to be rendered to God, the joy which is proper to the Lord's Day, or the proper relaxation of mind and body.
1. The precept of participating in the Mass is satisfied by assistance at a Mass which is celebrated anywhere in a Catholic rite either on the holy day or on the evening of the preceding day.
2. If because of lack of a sacred minister or for other grave cause participation in the celebration of the Eucharist is impossible, it is specially recommended that the faithful take part in the liturgy of the word if it is celebrated in the parish church or in another sacred place according to the prescriptions of the diocesan bishop, or engage in prayer for an appropriate amount of time personally or in a family or, as occasion offers, in groups of families.
Since a "grave cause" is needed to excuse one from this obligation it would be a serious or mortal sin to willfully skip Mass on Sunday or a Holy Day of Obligation, as the Church has always taught. Reasons such as the necessity to work to support one's family, child care, personal sickness or the care of the sick, necessary travel etc. would excuse a person on a particular occasion. Those who have continuing reason to be excused should consult their pastor.
If a priest is not available in an area and only a Liturgy of the Word or a Communion Service is offered the Mass obligation does not "transfer" to such services. As canon 1248 notes, participation is recommended for the spiritual value, especially if Communion is distributed.
The proper way to celebrate Sunday is spoken of at length in the Catechism of the Catholic Church.
Participation in the communal celebration of the Sunday Eucharist is a testimony of belonging and of being faithful to Christ and to his Church. The faithful give witness by this to their communion in faith and charity. Together they testify to God's holiness and their hope of salvation. They strengthen one another under the guidance of the Holy Spirit.
"If because of lack of a sacred minister or for other grave cause participation in the celebration of the Eucharist is impossible, it is specially recommended that the faithful take part in the Liturgy of the Word if it is celebrated in the parish church or in another sacred place according to the prescriptions of the diocesan bishop, or engage in prayer for an appropriate amount of time personally or in a family or, as occasion offers, in groups of families."
A day of grace and rest from work.
Just as God "rested on the seventh day from all his work which he had done," human life has a rhythm of work and rest. The institution of the Lord's Day helps everyone enjoy adequate rest and leisure to cultivate their familial, cultural, social, and religious lives.
On Sundays and other holy days of obligation, the faithful are to refrain from engaging in work or activities that hinder the worship owed to God, the joy proper to the Lord's Day, the performance of the works of mercy, and the appropriate relaxation of mind and body. Family needs or important social service can legitimately excuse from the obligation of Sunday rest. The faithful should see to it that legitimate excuses do not lead to habits prejudicial to religion, family life, and health.
The charity of truth seeks holy leisure - the necessity of charity accepts just work.
Those Christians who have leisure should be mindful of their brethren who have the same needs and the same rights, yet cannot rest from work because of poverty and misery. Sunday is traditionally consecrated by Christian piety to good works and humble service of the sick, the infirm, and the elderly. Christians will also sanctify Sunday by devoting time and care to their families and relatives, often difficult to do on other days of the week. Sunday is a time for reflection, silence, cultivation of the mind, and meditation which furthers the growth of the Christian interior life.
Sanctifying Sundays and holy days requires a common effort. Every Christian should avoid making unnecessary demands on others that would hinder them from observing the Lord's Day. Traditional activities (sport, restaurants, etc.), and social necessities (public services, etc.), require some people to work on Sundays, but everyone should still take care to set aside sufficient time for leisure. With temperance and charity the faithful will see to it that they avoid the excesses and violence sometimes associated with popular leisure activities. In spite of economic constraints, public authorities should ensure citizens a time intended for rest and divine worship. Employers have a similar obligation toward their employees.
In respecting religious liberty and the common good of all, Christians should seek recognition of Sundays and the Church's holy days as legal holidays.