Why is it mortal sin to miss Mass on Sundays?

The Catholic Answers

Christ said, “If thou wilt enter into life, keep the commandments.” Now one of these commandments is, “Remember that thou keep holy the sabbath day.” Thus God demands the sanctification of one day in seven in a special way. His very use of the word “Remember” implies a grave obligation not to forget or omit this duty. It is a mortal sin to disobey God in this matter. But how are we Christians to observe this commandment? Who is to tell us? Our Lord says, “If a man will not hear the Church, let him be as the heathen.” Matt. XVI11., 17. We must, then, hear the Church. Now the Catholic Church tells us that the central factor in the religion of Christ is the Mass, and that the chief thing in the sanctification of Sunday is to be present at the offering of that Sacrifice to God. This obliges under pain of mortal sin, unless sickness or other grave difficulties prevent such assistance at Mass. Remember that men are not only individual beings. They are also social units in a collective nation. And as they are obliged to worship God in their individual capacity, so too collectively. God has always demanded public worship, and from the earliest Apostolic limes Christians met regularly for religious exercises in common.

Radio Replies Volume 1 by Rev. Dr. Leslie Rumble MSC and Rev. Charles Mortimer Carty