The Torah forbids creative labor on the Sabbath. The Rabbis attempted to carefully define the major categories of work since accidental violation of the Sabbath would require the bringing of a sin offering (when the Temple stood) for each category violated.

7:1 They have laid down a general rule for the Sabbath: Whoever utterly forgets the essence of the Sabbath and commits many acts of (forbidden) labor on many Sabbaths is liable for only one sin-offering. Whoever is aware of the essence of the Sabbath and commits many acts of (forbidden) labor on many Sabbaths is liable for each and every Sabbath. Whoever knows that it is the Sabbath and commits many acts of (forbidden) labor on many Sabbaths is liable for each and every category of labor. Whoever commits many acts of (forbidden) labor within one category of work is only liable for one sin-offering.

7:2 The categories of work are forty less one (i.e., thirty-nine): one who sows, plows, reaps, or gathers; who threshes or winnows; one who selects, grinds, sifts, kneads, or bakes; one who shears wool, washes it, cards it, colors it, spins, or weaves it; one who makes two loops, or weaves two threads, or removes two threads from the loom; one who ties, or unties, or sews two stitches; one who tears in order to sew two stitches; one who traps a deer, slaughters it, skins it, salts it, cures the hide, scrapes it, or cuts it up; one who writes two letters and one who erases in order to write two letters; one who builds or destroys; one who extinguishes or ignites; one who strikes with a hammer; one who carries from one domain to another. Behold, these are the categories of work, forty less one.

60. Trans. S. Berrin.