"On the seventh day you shall rest." (Shemos 23:12)
It is a mitzvah to refrain from all forms of creative work on Shabbos, in
order to demonstrate that Hashem is the Creator and Controller of the
entire universe. There are thirty-nine primary forms of labor which we
are obligated to refrain from on Shabbos.
This mitzvah is the fourth of the Ten Commandments, which are listed twice
in the Torah, once in Parshas Yisro and once in Parshas Va'eschanan. The
wording is slightly different the second time around. The first time it
says, "Remember the day of Shabbos" (see mitzvah 59 above), while the
second time it says, "Guard the day of Shabbos." Our Sages explain
that "remember" refers to the positive mitzvos of eating and celebrating,
while "guard" refers to avoiding work. Both words were said by Hashem at
the same time to teach us that we need to perform both aspects of the
mitzvah in order to gain all of the intended benefits from Shabbos.
"Shabbos is equal to all of the other mitzvos." (Rashi, Bemidbar 15:41)