Of the Ten Mitzvot (or Commandments), only the fourth dictates a specific ritual. The text states, roughly translated from the Hebrew, "Remember the day of rest for its holiness" (zakhor et yom shabat l'kodsho). For thousands of years, this has been interpreted to mean that the seventh day of the week should be reserved for some sort of religious observance, the rituals we now simply call Shabbat. The rituals of Shabbat have come to include many things both at home and at the synagogue. But why is this observance so important that it deserves to be mentioned alongside the very moral core of Jewish philosophy?
The rest of the Ten Commandments are fairly simple and straightforward. They describe individual things people should or should not do in order to maintain a righteous and peaceful society. The tradition of Shabbat is no less essential, though it is considerably more complex. In short, Shabbat is a means to keep a community together. This requires specific attention paid to many different levels of our social and personal lives.
The most inclusive aspect of Shabbat is the weekly service at the synagogue. It is at this time that a vicinity's entire Jewish community is meant to come together, both to receive the next lesson in their continuing religious education and to spend time with those friends and acquaintances they might otherwise not see over the course of the week. This keeps Jews connected with other Jews just as it keeps Jews connected with the Torah. By singing, praying and eating together, Jews form a unique, lasting bond with one another during Shabbat.
Just as important as the Shabbat service is the Shabbat meal. This more often includes just close friends and family, hosted in a home rather than in a public place. Insisting upon a formal but friendly Friday night dinner makes sure that a family (especially in this busy, modern era) spends time together. Making the meal special makes it something to look forward to, differentiating it from the hum-drum dinners of work-weary weekdays.
On the most personal level, Shabbat is a time when each Jew can relax and reflect on the week as an individual. Though so much of Jewish culture revolves around community and family, it's still necessary for a person to decompress on his or her own. Shabbat, at its best, is supposed to be a time of comfort and relaxation. Though there are no formal rituals about the responsibility one has to one's self on Shabbat, it's well within the spirit of the day to indulge in those things that relieve stress and give one a sense of peace.
Without a day dedicated to rest and reaffirmation, a Jewish community simply doesn't work. As the commandment implies, Shabbat is a vague but necessary ritual. Its specifics may change with time but its core value is always the same.