The Torah teaches that the paschal lamb should be consumed in its entirety and any leftovers — including inedible parts — must be burned. A mishnah on today’s daf informs us that the burning takes place after the festival, by which it means the first day of Passover (the 15th of Nisan) which is a sacred day on which most labors are forbidden. Instead, the leftovers are burned on the 16th of Nisan (or on the 17th, if the 16th is Shabbat). The Gemara is curious about why this is so. After all, we learned that paschal lambs can be slaughtered on Shabbat. Why not burn the leftovers then, too? Isn’t that a positive biblical commandment and part of the mitzvah as well?
And why isn’t the leftover of the paschal lamb burned on the festival day itself? The positive mitzvah to burn the leftover should come and override the prohibition that prohibits the performance of labor on festivals.
We’ve dealt with this issue before concerning the obligation to circumcise a male newborn on the 8th day of life. While the sages limit our ability to complete tasks on Shabbat that may be completed in advance, the circumcision itself (a positive commandment) can be performed on Shabbat and on festivals. So why is this not the case for burning paschal leftovers?
The Gemara provides four answers that justify the ruling of the mishnah (spoiler alert: answer four appears at the top of page 85).
Answer #1: Hizkiya cites Exodus 12:10: And you shall not leave any of it until morning; and that which remains of it until morning you shall burn with fire. He notes the repetition of the words “until morning.” What can we learn from this? That the burning can take place on two different mornings, the 16th and the 17th, when the 16th is Shabbat.
Answer #2: Abaye cites Numbers 28:10 which says: the burnt-offering of each Shabbat on its Shabbat. This suggests that we can only burn offerings on Shabbat that are part of the Shabbat sacrifices. Thus, the burning of the leftovers from Passover must be delayed to the 17th.
Of course, these solutions explain why the burning must be deferred when Shabbat falls on the 16th, but do not explain why one can’t burn leftovers on the festival itself, on the 15th. And so, the Gemara keeps searching.
Answer #3: Rava cites Exodus 12:16, which states concerning festivals: no kind of labor shall be done on them, save that which every man must eat, only that may be done for you. This verse is the source that allows for the preparation of food on festivals, but only preparation. Therefore, the burning must be deferred.
Answer #4: Finally, Rav Ashi provides additional logic, arguing that a positive commandment (something you must do, such as burning the Passover leftovers) might in some cases override a negative commandment (something you must not do, such as perform labor on Shabbat and festivals). However, in this particular case we have a positive commandment (burning) competing against both a negative commandment (the prohibition of labor on Shabbat and festivals) and a positive commandment (one’s obligation to rest on Shabbat and festivals). And, he concludes, in this case that positive commandment (burning) does not override the one-two punch of both a prohibition (labor) and a positive commandment (rest) — so the burning must be delayed.
It’s clear that the Gemara is interested in preserving the ruling of the mishnah that one may only burn paschal leftovers on a weekday — neither Shabbat nor the first day of Passover which is a festival. It’s also clear that there was no single accepted tradition about why, so the Talmud here generates a number of explanations.