Precepts of the Church
The First Precept: You shall attend Mass on Sundays and on holy days of obligation and rest from servile labour.
The first precept, as based on the third commandment, requires the faithful to sanctify the day of commemorating the resurrection of the Lord as well as the principal liturgical feasts honouring the mysteries of the Lord, the Blessed Virgin Mary, and the Saints: in the first place by participating in the Eucharistic celebration, in which the Christian community is gathered, and by resting from those works and activities which could impede such a sanctification of these days.
Missing Mass without a serious reason is a mortal sin. As Catholics we believe that the Mass is the highest form of prayer and worship. The catechism tells us “the Sunday Eucharist is the foundation and Confirmation of all Christian practice”. CCC 2181. Sunday is the day of rest. Servile labour should be left to the other six days. Though it may not be possible to attend Mass on Sundays, the Saturday vigil is another acceptable option for committing to the first precept and therefore the third commandment.