Beitzah 15 - Does one have to eat on a Holiday?
If the Holiday (Yom Tov) is followed by Shabbat, then people who are celebrating the Yom Tov may completely forget about Shabbat, and finish all the provisions and drinks, coming to Shabbat with nothing to eat. In order that this should not happen, the Sages instituted a reminder in the form of "food mix," or "eruvei tavshilin." This food eruv is prepared before the Yom Tov, by taking some foods in one's hand and declaring "with this eruv (which I will eat on Shabbat) it becomes permitted to me to cook on a Yom Tov for the needs of Shabbat." Normally cooking on a Yom Tov for Shabbat is forbidden, but with this eruv this, too, becomes allowed.
Once Rabbi Eliezer was giving a lecture about the laws of Yom Tov, the whole day of Yom Tov. A group of students arose and left, and Rabbi Eliezer commented, "They must have prepared barrels of wine, and are rushing to drink it." When the second group left, he said, "They have casks of wine." When the sixth group left, he said, "These are desolate people." Some students, however, remained till the conclusion, and to them he said, " Go and eat rich food, drink sweet beverages, and do not be melancholy ."
Why was Rabbi Eliezer so strict with his students? After all, there is a mitzvah to eat and drink and be merry on a Yom Tov? - He disagrees with this requirement: all the time that one is engaged in Torah study, it takes preference, and only when he stops - then the obligation to eat and drink devolves on him.
Art: A Kitchen Still Life With A Servant Boy Holding A Cask Of Wine by (after) Michelangelo Merisi Da Caravaggio