To eat the roasted flesh of the Passover offering on the night of the fifteenth of Nisan

That is that He commanded us to eat the lamb of the Pesach-offering on the night of the fifteenth of Nissan according to the stipulations mentioned - and that is that it is roasted, that it is eaten in one house and that is eaten with matzah and bitter herbs (maror). And that is His saying, "They shall eat the meat that night; they shall eat it roasted with fire, with matzah and with bitter herbs" (Exodus 12:8). And perhaps a questioner will challenge me and say, "Why do you count the eating of the Pesach-offering, matzah and the bitter herbs as one commandment and not count them as three commandments?" I would [then] answer him that it is true that the eating of matzah is a separate commandment, as I will explain later (Sefer HaMitzvot, Positive Commandments 158); likewise is the eating of the meat of the Pesach-offering a separate commandment, as we have mentioned. However the bitter herbs are an extension of the eating of the Pesach-offering and are not counted as a separate commandment. And the proof of the matter is that the meat of the Pesach-offering is eaten to fulfill the commandment, whether bitter herbs are available or whether they are not available. But bitter herbs are only eaten with the meat of the Pesach-offering - as His saying, "upon [...] bitter herbs shall they eat it" (Numbers 9:11). But [if one ate] bitter herbs without meat, he has not done anything; and we do not say that he has already fulfilled a commandment. And the language of the Mekhilta (Mekhilta d'Rabbi Yishmael 12:8:3) is, "'They shall eat it roasted with fire, with matzah and with bitter herbs' - tells [us] that the commandment of the Pesach-offering is roasted meat, matzah and bitter herbs." This means that the commandment is the combination of these. And there, they said, "From where [do we know that] which you say, that if they do not have matzah and bitter herbs, they fulfill their obligation with the Pesach-offering? [Hence] we learn to say, 'shall they eat it'" - meaning the meat by itself. "I might think that if they do not have a Pesach-offering, they [do not] fulfill their obligation with matzah and bitter herbs. Behold you argue: The Pesach-offering is a positive commandment and matzah and bitter herbs are a positive commandment. Behold you have learned that if they do not have matzah and bitter herbs, they fulfill their obligation for the Pesach-offering; so too, if they do not have the Pesach-offering, they fulfill their obligation for matzah and bitter herbs. ([Hence] we learn to say, 'upon matzah and bitter herbs shall they eat it.')" And there, they [also] said, "'They shall eat it' - From here, [we know] that the Pesach-offering is to be eaten in a state of satiety, but matzah and maror are not [necessarily] to be eaten in a state of satiety." That is because the essence of the commandment is the eating of the meat - as He said, "They shall eat the meat that night," whereas the bitter herbs are an extension of the eating of the meat; and their obligation is explained from these verses, for those that understand them. And the obvious proof of this is the [following statement] in the Talmud - and that is their saying (Pesachim 120a), "Bitter herbs in our days is rabbinic." For there is no obligation from the Torah to eat them by themselves. Rather they should be eaten with the meat of the Pesach-offering. And that is a clear proof that they are from those things that are extensions of the commandment [of the Pesach-offering], and that their eating is not a separate commandment. And the regulations of this commandment are also explained in Tractate Pesachim. (See Parashat Bo; Mishneh Torah, Paschal Offering 1.)