Overeating on Passover is a mitzvah TB Pesakhim 70

The Haggigah (חגיגה) sacrifice is a special and unique offering. It is a peace well-being sacrifice (שלמים) that is offered up and then eaten to celebrate and enjoy on the three pilgrimage holidays, Passover, Shavuot, and Sukkot. It is an individual’s sacrifice; however, it is also considered like a public sacrifice because all of Israel is bringing his own Haggigah. Only animals and not fowls or meal offerings are acceptable as a Haggigah. There is a whole massekhet dedicated to this topic which we will start studying in just over a year from now. On erev Passover, there is a non-obligatory sacrifice that is called the Haggigah of the 14th (of Nisan). The Mishnah is discussing this non-obligatory Haggigah.

There are two possible versus where the rabbis expounded the mitzvah of the korban Haggigah. The first possibility is “וְהָיָה֩ הַיּ֨וֹם הַזֶּ֤ה לָכֶם֙ לְזִכָּר֔וֹן וְחַגֹּתֶ֥ם אֹת֖וֹ חַ֣ג לַֽיהוָ֑ה לְדֹרֹ֣תֵיכֶ֔ם חֻקַּ֥ת עוֹלָ֖ם תְּחָגֻּֽהוּ:-This day shall be to you one of remembrance: you shall celebrate it as a festival to the LORD throughout the ages; you shall celebrate it as an institution for all time.” The word  וְחַגֹּתֶ֥םis reference to the Haggigah.1 Today’s daf TB Pesakhim 70 suggests the second possible source. “Rav said: What is ben Dortaif’s reason? As it is written: ‘And you shall slaughter the Paschal offering to the Lord your God from the flock and from the herd, in the place which the Lord shall choose to rest His name there’ (Deuteronomy 16:2). A question must be asked: Does the Paschal offering come from the herd, i.e., from cattle? Doesn’t the Paschal offering come from only the sheep and from the goats, as commanded in the book of Exodus (12:5)? Rather, the verse should be understood as follows. ‘Flocks’- this is referring to the Paschal offering. ‘Herd’; this is referring to the Festival peace-offering that is brought along with it.’” (Sefaria.org translation)

You may be wondering why the Gemara is discussing the Haggigah of the 14th  now. The first Mishnah of chapter delineated what aspects of the korban Pesakh supersede Shabbat and which aspects don’t when the 14th of Nisan falls on Shabbat. The next Mishnah found that the very bottom of TB Pesakhim 69 brings up the korban Haggigah because it doesn’t supersede the Shabbat at all.

“When, however, the Paschal lamb comes on Shabbat, or when few people are registered for it so that each person will receive a large portion, or when it is brought in a state of ritual impurity, one does not bring a Festival peace-offering with it.” (Sefaria.org translation) The Mishnah includes lots of other details about this sacrifice.

The Gemara teaches us which sacrifice, the korban Pesakh or the korban Haggigah, is is in first and why. “The Gemara asks: If there is no obligation to bring this offering, what is the reason that it nevertheless comes when each person’s portion of the Paschal lamb is small? The Gemara explains that the reason is as it was taught in a baraita: The Festival peace-offering that comes with the Paschal lamb is eaten first; the reason for this is so that the Paschal lamb will be eaten when one is already satiated. The Paschal lamb should not be eaten in a needy manner, but rather in joy and when one is already filled to satisfaction.” (Sefaria.org translation) 

This has to be the source of the tradition where people who prepare the food for the Seder night make so much food that we overeat beyond satisfaction.