Question: What does the 3rd commandment really mean — to keep holy the Sabbath day? It seems we have reduced it down to attending Mass for 45 minutes a week on a Sunday. People work regularly, use Sunday as a day of leisure, sports entertainment, whatever. I've looked at the catechism and it seems a little wishy-washy to me, especially since this is a commandment.
Discussion: Thank you for this excellent question, not only because of its importance in drawing closer to God but also its timeliness as we consider our priorities, choices, and activities for the New Year.
Keeping the Sabbath holy first means worshiping God, not just anywhere but within the Church where — in body, mind, and spirit — we take part in the Body of Christ. Attending Mass sometime between Friday night and sundown Saturday would be in keeping with the Sabbath hours originally set for the seventh day of rest. For a once-a-week assembly though, the Catechism established what most Christians continue to do: Come together each Sunday in honor of our Resurrected Lord's first appearance on Easter. This special time of receiving Eucharist truly re-Members the Sabbath as Members of the Body of Christ become one through Christ's own body and blood.
As you pointed out though, Mass may take only 45 minutes, so what about the remaining hours? Do we still have to keep the whole day holy to the Lord? In some ways, every day needs to be holy to God, for instance, by praying, forgiving, and seeking God's will in our lives. However, Hebrews 4:9-10 addresses need for more than this by saying, "So then, there remains a Sabbath rest for the people of God; for whoever enters God's rest also ceases from his labors as God did from his" (Revised Standard Version.) You might say, then, that remembering the Sabbath is a time to forget our own work or anything that's part of our regular workday routines and, instead, focus on God's work in and around us.
At first peek, the Catechism seems to offer little guidance on how we're to go about this, but actually, its contents have been as highly compressed as a poem, which often requires three or more readings to reveal its mysteries. At any reading rate, the Subject Index of the Catechism lists a number of references under "Sabbath, Sabbath rest," while Article 3 of "Part Three: Life In Christ" focuses entirely on "The Third Commandment." Each of those several pages warrants a prayerful and careful reading, but the subheading, "A day of grace and rest from work," offers the most direct response to your question.
For instance, 2184 says: "Just as God 'rested on the seventh day from all his work which he had done,' human life has a rhythm of work and rest. The institution of the Lord's Day helps everyone enjoy adequate rest and leisure to cultivate their familiar, cultural, social, and religious lives." That word "cultivate" emphasizes the ongoing need to nurture the relationships vital to a well-rounded life — a life meant to include family, community, society, and religion. With those key words to direct us, we begin to see some personal answers for appropriate use of our prime-time Sundays. And I say "personal" because God gives each of us a variety of gifts and a variety of options for using them. So, depending on each unique combination of our spiritual gifts and means, we might feel led, for instance, to spend time in prayer, take Eucharist to a home-bound parishioner, go on a "date" with our spouse, phone a family member, visit a child in the hospital, invite a lonely neighbor to lunch, baby-sit for an overwhelmed parent, attend a concert of uplifting music, participate in a Bible study group, restore something in the environment, or make amends in a broken relationship. Seldom, however, will any single individual do all of the above since remembering the Sabbath also remembers our own need to rest.
Generally speaking, the Catechism says, "On Sundays and other holy days of obligation, the faithful are to refrain from engaging in work or activities that hinder the worship owed to God, the joy proper to the Lord's Day, the performance of the works of mercy, and the appropriate relaxation of mind and body…" (2185.) After reminding us to be mindful that other people need rest too, 2186 goes on to say, "Sunday is traditionally consecrated by Christian piety to good works and humble service of the sick, the infirm, and the elderly. Christians will also sanctify Sunday by devoting time and care to their families and relatives, often difficult to do on other days of the week. Sunday is a time for reflection, silence, cultivation of the mind, and meditation which furthers the growth of the Christian interior life." So, regardless of whether our regular workweek has taxed us physically, mentally, or spiritually, a day of Sabbath rest encourages us to rest — in every way — in God.