Shabbat
For six days you may perform melachah (work), but the seventh day is a complete Sabbath, holy to the LORD ... it is an eternal sign that in six days, the LORD made heaven and earth, and on the seventh day he rested and was refreshed.
Exodus 31:15-17
The Nature of Shabbat
The Sabbath (or Shabbat, as it is called in Hebrew) is one of the best known and least understood of all Jewish observances. People who do not observe Shabbat think of it as a day filled with stifling restrictions or as a day of prayer like the Christian Sabbath. But to those who observe Shabbat, it is a precious gift from God, a day of great joy eagerly awaited throughout the week, a time when we can set aside all of our weekday concerns and devote ourselves to higher pursuits. In Jewish literature, poetry and music, Shabbat is described as a bride or queen, as in the popular Shabbat hymn Lecha Dodi Likrat Kallah (come, my beloved, to meet the [Sabbath] bride). It is said "more than Israel has kept Shabbat, Shabbat has kept Israel."
Shabbat is the most important ritual observance in Judaism. It is the only ritual observance instituted in the Ten Commandments. It is also the most important special day, even more important than Yom Kippur. This is clear from the fact that more aliyot (opportunities for congregants to be called up to the Torah) are given on Shabbat than on any other day.
Shabbat is primarily a day of rest and spiritual enrichment. The word "Shabbat" comes from the root Shin-Beit-Tav, meaning to cease, to end, or to rest. Shabbat is not specifically a day of prayer. Although we do pray on Shabbat, and spend a substantial amount of time in synagogue praying, prayer is not what distinguishes Shabbat from the rest of the week. Observant Jews pray every day, three times a day. To say that Shabbat is a day of prayer is no more accurate than to say that Shabbat is a day of feasting: we eat every day, but on Shabbat, we eat more elaborately and in a more leisurely fashion. The same can be said of prayer on Shabbat.
In modern America, we take the five-day work-week so much for granted that we forget what a radical concept a day of rest was in ancient times. The weekly day of rest has no parallel in any other ancient civilization. In ancient times, leisure was for the wealthy and the ruling classes only, never for the serving or laboring classes. In addition, the very idea of rest each week was unimaginable. The Greeks thought Jews were lazy because we insisted on having a "holiday" every seventh day.