DEUT1545 The second [reason] [I.e., For the mitzvah to eat a set meal on the day before Yom Kippur]--on every other Yom Tov we eat a set meal for the joy of the mitzvah. The reward for feeling joy in fulfilling the mitzvos is very great and exalted, as the pasuk says (I Divrei Hayamim 29:17), "Now I have seen Your people, who are present here; with joy they have donated to You." [This is referring to the outpouring of donations for the building of the Beis HaMikdash. The next pasuk goes on to say, "Hashem...keep this forever," and Rashi comments, "Evoke, on our behalf, this donation as a great mitzvah."] The pasuk also says [this verse], "[These curses will come upon you…] because you did not serve Hashem, your God, with joy and goodness of heart." [We can infer from this that great blessing comes to those who fulfill the mitzvos out of joy.] Since we must fast on Yom Kippur, we are required to eat the set meal [that is associated] with the joy of the mitzvah [I.e., The mitzvah of observing the Yom Tov of Yom Kippur] instead.