" 'Sunday . . . is to be observed as the foremost holy day of obligation in the universal Church' (CIC, can. 1246 § 1). 'On Sundays and other holy days of obligation the faithful are bound to participate in the Mass' (CIC, can. 1247)."
"The first precept ('You shall attend Mass on Sundays and holy days of obligation and rest from servile labor') requires the faithful to sanctify the day commemorating the Resurrection of the Lord as well as the principal liturgical feasts honoring 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.
"The second precept ('You shall confess your sins at least once a year') ensures preparation for the Eucharist by the reception of the sacrament of reconciliation, which continues Baptism's work of conversion and forgiveness.
"The third precept ('You shall receive the sacrament of the Eucharist at least during the Easter season') guarantees as a minimum the reception of the Lord's Body and Blood in connection with the Paschal feasts, the origin and center of the Christian liturgy."
-- CCC 2042