The 159th mitzvah is that we are commanded to refrain from doing melachah on the first day1 of Pesach.

The source of this commandment is G‑d's statement (exalted be He),2 "The first day [of Pesach] shall be a sacred holiday."

Keep in mind the following introduction: in every case where the Torah says, "sacred holiday" [mikra kodesh], our Sages explain that the intention is, "one must sanctify it" [kadsheihu]. This means that one may not do any melachah unless it involves preparation of food, as explained in Scripture.3

We have already explained4 the statement of our Sages, "The term Shabbason indicates a positive commandment," i.e., for every day which is called Shabbason, it is as if it is written, "rest," or "you shall rest," all being commands to cease melachah. [A similar phrase,] Shabbsos Hashem,5 is used to refer to all the "special times," i.e., the Yomim-Tovim.

In many places in the Talmud6 it is said, "Yom-Tov is both a positive and a negative commandment." This means that refraining from melachah on every Yom-Tov is a positive commandment, and doing a prohibited melachah on Yom-Tov is a prohibition. Therefore, anyone who performs a melachah on Yom-Tov transgresses both a positive and a negative commandment.

The details of refraining from these types of melachah are explained in Tractate Yom-Tov [i.e., Beitzah].