Shabbat is a day of holiness, set apart and elevated above the rest of the week. The special laws pertaining to Shabbat preserve its sanctity and beauty.
The unique quality of Shabbat derives from two types of mitzvot: the mitzvot of sanctification such as candle-lighting and Kiddush; and the equally important mitzvot which require that we refrain from certain activities and work. The prohibitions against "work," far from being negative or burdensome, are an integral part of the experience of Shabbat as a day when body and soul are in true harmony.
These two aspects of Shabbat are reflected in the two expressions found in the two different presentations of the Ten Commandments found in the Torah. "Remember the Sabbath to keep it holy..." (Exodus 20:8) and "Guard the Sabbath to keep it holy..." (Deuteronomy 5: I 2) were, according to tradition, heard simultaneously by the Jewish people at Mount Sinai.
Zachor, "remember," refers to the positive commandments of the day--the things we do. Shamor, "guard," refers to the negative commandments--the things we may not do. The latter, including such activities as cooking, writing and turning lights on and off, are described generally by the word melachah, a certain type of work.
The Hebrew language has two words for "work"--avodah and melachah. Avodah is a general term meaning work, while melachah has a very precise halachic meaning. On Shabbat, melachah is prohibited. Our Sages explain that melachah refers to the activities which were necessary for construction of the Mishkan, the traveling sanctuary which the Jews took with them throughout their desert wanderings.
The Torah specifically mentions two melachot, kindling a fire and carrying. The Mishnah further explains that 39 different categories of melachah went into building the Mishkan. While these categories of labor refer to the construction of the Mishkan, they actually encompass all forms of human productivity. These melachot are not a haphazard collection of activities, and do not necessarily represent physical exertion. Rather, the principle behind them is that they represent constructive, creative effort, demonstrating man's mastery over nature. Refraining from melachah on Shabbat signals our recognition that, despite our human creative abilities, G‑d is the ultimate Creator and Master.
A newcomer to Shabbat observance may be concerned that the numerous laws and their many nuances would present a hindrance to oneg Shabbat--enjoying and delighting in Shabbat. However, the unique way in which we pursue ordinary activities on Shabbat actually serves as a constant reminder of the special nature of this day. Refraining from so many of the activities that we take for granted during the week heightens our awareness that Shabbat is different from the other days of the week, and creates a whole new frame of mind for Shabbat.