Even though this is the seventh day of every week (counting from Sunday), and there are over 50 such days each year, Shabbat is a holy day - and even one of the most important holy days in Judaism. In fact, apart from the Day of Atonement (Yom Kippur,) Shabbat is the holiest day for Jews, and is the only one mentioned in the Ten Commandments.
The observance of Shabbat has always been central to the Jewish people’s experience and existence, at least until recent generations. A well-known saying states that more than the Jewish people have kept Shabbat, Shabbat has kept the Jewish people.
According to ancient Jewish tradition, Shabbat has a clear connection to the creation of the world: on the seventh day God rested (“Shabbat,” in Hebrew) from the work of creation, so this is a holy day for men, and they, too, are to rest from productive work.
The idea of Shabbat - one day sanctified for rest after six days of toil - is one of the important contributions of Judaism to world culture. It is also the basis for the concept of the week as a cyclical unit of time. The Jewish Shabbat served as a model for the setting of the holy day for Christians (Sunday) and for Muslims (Friday).
In the Jewish calendar, the days are counted from the sunset of one day until sunset the following day. Shabbat therefore begins on Friday evening, called Erev Shabbat, and ends on Saturday evening, called Motsa’ei Shabbat. The exact times of the beginning and end of Shabbat are determined in advance and change from week to week and from place to place.
The customs associated with Shabbat are many and varied. First and foremost, it is a day of rest, on which all productive work is forbidden. According to Jewish law, any activity connected with fire is forbidden, and religious Jews do not turn electricity on or off on Shabbat and do not travel. Many other Jews, who define themselves as traditional (and who are moderately religious), also partially avoid traveling, using electricity or performing other types of productive work. Many of them do not answer the telephone on Shabbat.
For religious Jews, Shabbat is a day filled with prayer, and they spend many hours in the synagogue. Part of the Shabbat prayer service in the synagogue is the reading of the Torah (the first five books of the Bible - Genesis, Exodus, Leviticus, Numbers and Deuteronomy). Throughout the year, a portion of the Torah is read each week. Incidentally, the division of the Torah into weekly portions is the original ancient division; the division into chapters came later.
Over the course of an entire year, Shabbat after Shabbat, the entire Torah is read. The completion of the reading of the Torah is on a day that may not necessarily be Shabbat: the eighth day of the Festival of Sukot (called Shmini Atseret), is also the Festival of Rejoicing in the Torah (Simkhat Torah). That day also marks the start of the reading of the Torah from the beginning again.