Yom Kippur, the holiest of days, has two diametrically opposed halachot. There is a strict requirement to "afflict" ourselves. On the other hand, Chazal relate great importance to eating on the day before it.
R. Yehoshua ben Chananya tried to learn from the pasuk, "You [Moshe] are going to lie with your fathers, and the nation will get up and act licentiously" (Devarim 31:16) that there is resurrection of the dead (it can be read, with difficulty, that Moshe will get up) and that Hashem knows what will happen in the future. He settles at the end that the pasuk proves only the latter, but why would one consider to read the pasuk referring to resurrection, which seems to "abuse" the pasuk?
[In the next section, Rav Yisraeli takes the people of his generation to task for certain important shortcomings in the national sphere. While this contains important lessons, we will not focus on them at this time.]
The Jewish People has almost unlimited ability to grow spiritually because they can use even that which is mundane in the world for sanctity. When Moshe was on Sinai for 40 days and nights without eating and drinking, it was not that he did not need sustenance, but that the sustenance came from the Divine Presence (see Shemot Rabba 47:7). Man is not sustained by bread alone but on all that comes from Hashem’s ‘mouth’ (see Devarim 8:3), as everything in the world is spiritual. It is just that we are not able to digest in that way, although Moshe was able to.
On Yom Kippur, there is a shadow of Moshe’s level in all of us, as this was the day that Moshe came down from Sinai the final time. The essence of the fast is refraining from physical activity, and we raise ourselves to the level of angels. That is why the haftara focuses on fasting, in a manner that discusses increased activity. For it is not a fast of lack of energy but of obtaining power through spiritual means. That is also why stress is placed on eating on Erev Yom Kippur. It is to teach that it is all the same. We can use the spiritual ‘food’ of the fast day the way we used the regular food the day before. Even though we cannot always be sustained in this manner, we must know that from the perspective of what Hashem provides, it is possible.
These ideas also explain why Bnei Yisrael falls steeply at times. We have a great appetite for spiritual food, but when we are not able to find it, we go looking for things that remind us of it. Simple avoda zara like other nations do does not suffice for a misguided Jew, as he is looking for more, even if it is in a more dangerous way.
For this reason, when Moshe died and was lost to Israel, the nation got up and adopted licentious tendencies in the broadest sense. The discussion of resurrection of the dead was not about physical death but about spiritual death. They need not stay dead; they can get up. That state is not natural for them, and they will be able to return to spiritual form.
What is needed is "great repentance, which reaches until His glorious throne" (Yoma 6:1). Not partial repentance, but one that transcends boundaries and impediments. We have experienced partial redemption, but that is not enough. We need geula shleima, a return to all of our spiritual greatness. This is what we pray for on these holy days.