Since they cannot receive communion in this state, are they still required to attend, but not participate in, Sunday Mass? Or is missing Mass, even in a state of mortal sin, committing another mortal sin.
The obligations to participate in the Mass and to receive the Eucharist are distinctly individual points of law.
Regarding participation in the Mass, *Code of Canon Law * (CIC) states, “On Sundays and other holy days of obligation, the faithful are obliged to participate in the Mass” (CIC 1247). (Note: “Participate” here means to at least be present and conscious.)
Concerning reception of the Eucharist, the Code states, “After being initiated into the Most Holy Eucharist, each of the faithful is obliged to receive holy communion at least once a year” (CIC 920).
Also, “A person who is conscious of grave sin is not to celebrate Mass or receive the body of the Lord without previous sacramental confession…” (CIC 916). (Note: “Celebrate” here means what the priest does.)
So Catholics are obligated to participate in the Mass on holy days of obligation (including Sunday) and to receive the Eucharist at least once a year. If a Catholic is unable to receive the Eucharist for any reason (including being conscious of grave sin) he is still obligated to participate in the Mass.
The Catechism of the Catholic Church (CCC) recognizes this when it considers the situation of divorced and civilly remarried Catholics. “If the divorced are remarried civilly, they find themselves in a situation that objectively contravenes God’s law. Consequently, they cannot receive Eucharistic communion as long as this situation persists… Toward Christians who live in this situation… [t]hey should be encouraged to listen to the Word of God, to attend the Sacrifice of the Mass… (CCC 1650-1651).