Answer:
The questions about Mass attendance and the reception of Holy Communion are clearly outlined in what are traditionally called the “Precepts” of the Church. These specific teachings are intended to stand alongside the Ten Commandments as fundamental practices for Catholics and are outlined in the Code of Canon Law. The obligations related to Mass attendance and receiving Communion are outlined in the first and third precepts, which we find quoted in the Catechism of the Catholic Church (no. 2042):
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 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.
Rather than seeing these as obligations that are simply to be fulfilled out of a sense of duty, Pope Saint John Paul II reminds us of the grace that is made available to us when we gather for Sunday celebrations of the Eucharist: “Sunday is the day which is at the very heart of the Christian life… Time given to Christ is never time lost, but is rather time gained, so that our relationships and indeed our whole life may become more profoundly human” (Dies Domini, no. 7).