Today, the laws are disappearing, relics of a time when Protestant culture was more dominant. Connecticut, for example, finally decided to permit Sunday liquor sales last year. And in the United States, Sunday has lost its sacred character. Most Christians see little conflict in going to church in the morning, then watching a football game — maybe with the family, or maybe at a sports bar — in the afternoon.

The Sabbatarian tradition is upheld, in a serious way, by some small groups of religious Protestants and, of course, by observant Jews. And, it so happens, by those who think of themselves as both Christian and Jewish. “Messianic Jews,” who believe in the divinity of Jesus but pay special attention to the Jewish roots of Christianity, are often very attached to Sabbath observance.

Sarah Posner, a staff writer for the ReligionDispatches.org Web site, recalled a conference of messianic Jews she attended last year in Ellicott City, Md. “They weren’t selling their books, CDs and DVDs on Saturday, because they didn’t want to exchange money,” Ms. Posner said. “But they were using electricity” — which traditionally observant Jews would not.

Our religiously diverse country includes those who call their weekly day off from smartphones a “secular Sabbath.” Some groups may not even have a concept of Sabbatarianism. In Islam, for example, “there’s a deep theological objection to the idea that God rested on the seventh day,” according to Marion Holmes Katz, a scholar of Islam at New York University. “The idea of God resting seems to imply God being tired. So the whole idea that you refrain from work as some sort of ritualized recapitulation or symbolic nod to the process of creation — it’s not one that has any traction in Islam.”

But in Catholicism, as Pope Francis suggests, the Sabbath actually is supposed to matter — the whole day, not just Mass. For as the catechism teaches, in Paragraph 2185, “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.”

The Catholic Church has been recovering this teaching at least since 1998, when Pope John Paul II published his apostolic letter “Dies Domini.” There, he writes that “even in those countries which give legal sanction to the festive character of Sunday, changes in socioeconomic conditions have often led to profound modifications of social behavior and hence of the character of Sunday.”