CCC 2181

The Sunday Eucharist is the foundation and confirmation of all Christian practice. For this reason the faithful are obliged to participate in the Eucharist on days of obligation, unless excused for a serious reason (for example, illness, the care of infants) or dispensed by their own pastor.¹¹⁹ Cf. CIC, can. 1245. Those who deliberately fail in this obligation commit a grave sin.