Is it a sin to go to a store, go out to dinner, or attend any type of entertainment event on a Sunday? If so, is it a mortal or venial sin?
It is not a sin—but neither should Sunday be treated as an ordinary day to catch up on things not done during the previous six days. The Lord rested on the sabbath, and so should we.
Rabbi Abraham Heschel wrote: “Six days a week we wrestle with the world, wringing profit from the earth; on the sabbath we specially take care of the seed of eternity planted in the soul. . . . Six days a week we seek to dominate the world; on the seventh we try to dominate the self” (I Asked for Wonder).
For almost 2,000 years, Christians have observed the Third Commandment on Sunday. International airline and nautical schedules—and some calendars—count Sunday as the seventh day of the week.