Halakhah zu Wajikra 23:7

The commandment of resting on the first day of Pesach: To rest on the first day of Pesach, as it states about it (Leviticus 22:7), "On the first day, a holy occasion." And about all about which it is stated in the Torah, "a holy occasion," they, may their memory be blessed, explained (Sifra, Emor, Chapter 12:4), "Make it holy." And the content of its holiness is that no work be done on it, except for that which is specific to eating; as the verse elucidated (Exodus 12:16), "but that which is eaten by every soul, that alone shall be done for you." And the proof that the rest of the holiday is considered a positive commandment is their, may their memory be blessed, saying (Shabbat 25a), "This 'shabbaton' is a positive commandment." And we learn from now that in every place that shabbaton is stated in the Torah with regards to a holiday, it is a positive commandment. And [what] also appears much in the Talmud is, "The holiday is a positive commandment and a negative commandment."

To not do work on the first day of Pesach: That we not do work on the first day of the holiday of Pesach - which is the fifteenth of Nissan - as it is stated (Leviticus 23:7), "On the first day, a holy occasion shall it be for you; all work of labor shall you not do." And Scripture already warned about this in the Order of Bo el Pharoah in the command of the holiday of Pesach; as it is stated there (Exodus 12:16), "all work shall not be done upon them." And Rambam, may his memory be blessed, brought that verse (in Sefer HaMitzvot LaRambam, Mitzvot Lo Taase 223) in his tally. But I have written this other one, so that the holidays be organized in one order. But it all comes to the same thing.

And the root of this commandment and all of its content is written in the previous commandment - which is the first day of Pesach (Sefer HaChinukh 298). However it is fitting, my son, that I elucidate for you the matter of two days for each and every appointed time, whereas our Torah only obligated us one holiday - as it is written explicitly about Peasch (Leviticus 23:7-8), "On the first day, a holy occasion," and "on the seventh day"; and so with [Shavuot] and Rosh Hashanah and Sukkot.