Yom Kippur is a Taste of the Future World
In Your abounding compassion, You have given us this fast day of Yom Kippur... A day on which it is forbidden to eat, forbidden to drink... — From the Mussaf prayer for Yom Kippur
In the World to Come, there is neither eating nor drinking... — Talmud, Berachot 17a
Man consists of a body and a soul - a physical envelope of flesh, blood, sinew and bone, inhabited and vitalized by a spiritual force described by the Chassidic masters as "literally a part of G-d above." 
Common wisdom has it that spirit is loftier than matter, and the soul holier (i.e., closer to the Divine) than the body. This conception seems to be borne out by the fact that Yom Kippur, the holiest day of the year - the day on which we achieve the height of intimacy with G-d - is ordained by the Torah as a fast day, a day on which we seemingly abandon the body and its needs to devote ourselves exclusively to the spiritual activities of repentance and prayer.
In truth, however, a fast day brings about a deeper, rather than more distant, relationship with the body. When a person eats, he is nourished by the food and drink he ingests. On a fast day, vitality comes from the body itself, from energy stored in its cells. In other words, on less holy days, it is an outside force (the energy in one's food and drink) that keeps body and soul together; on Yom Kippur, the union of body and soul derives from the body itself.
Yom Kippur thus offers a taste of the culminant state of creation known as the "World to Come."
The Talmud tells us that "in the World to Come, there is neither eating nor drinking" - a statement that is sometimes understood to imply that in its ultimate and most perfect state, creation is wholly spiritual, devoid of bodies and all things physical. 
Kabbalistic and Chassidic teaching, however, describe the World to Come as a world in which the physical dimension of existence is not abrogated, but is preserved and elevated. 
The fact that there is "neither eating or drinking" in the World to Come is not due to an absence of bodies and physical life, but to the fact that in this future world, "the soul will be nourished by the body" itself, and the symbiosis of matter and spirit that is man will not require any outside sources of nutrition to sustain it. 
The physical and the spiritual are both creations of G-d. Both were brought into being by Him out of utter nothingness, and each bears the imprint of its Creator in the particular qualities that define it.
The spiritual, with its intangibility and its transcendence of time and space, reflects the infinity and sublimity of G-d. The spiritual is also naturally submissive, readily acknowledging its subservience to a higher truth.  It is these qualities that make the spiritual "holy" and a vehicle of relationship with G-d.
The physical, on the other hand, is tactual, egocentric and immanent - qualities that brand it "mundane" rather than holy, that mark it as an obfuscation, rather than a revelation, of the divine truth. For the unequivocal "I am" of the physical belies the truth that "there is none else besides Him"  - that G-d is the sole source and end of all existence.
Ultimately, however, everything comes from G-d; every feature of His every creation has its source in Him and serves to reveal His truth. So on a deeper level, the very qualities that make the physical "unholy" are the qualities that make it the most sacred and G-dly of G-d's creations. For what is the "I am" of the physical if not an echo of the unequivocal being of G-d? What is the tactility of the physical if not an intimation of the absoluteness of His reality? What is the "selfishness" of t he physical if not an offshoot, however remote, of the exclusivity of the Divine expressed in the axiom "There is none else besides Him"?
Today, the physical world shows us only its most superficial face, in which the divine characteristics stamped in it are corrupted as a concealment, rather than a revelation, of G-dliness. Today, when the physical object conveys to us "I am," it bespeaks not the reality of G-d but an independent, self-sufficient existence that challenges, rather than reiterates, the divine truth. But in the World to Come, the product of the labor of a hundred generations to sanctify the material world toward a G-dly end, the true face of the physical will come to light.
In the World to Come, the physical will be no less a vehicle of divinity than the spiritual. In fact, in many respects, it will surpass the spiritual as a conveyor of G-dliness. For while the spiritual expresses various divine characteristics - G-d's infinity, transcendence, etc. - the physical expresses the being of G-d.
Today, the body must look to the soul as its moral guide, as its source of awareness and appreciation of all things divine. But in the World to Come, "the soul will be nourished by the body." The physical body will be a source of divine awareness and identification that is loftier than the soul's own spiritual vision.
Yom Kippur is a taste of this future world of reverse biology. It is thus a day on which we are "sustained by hunger,"  deriving our sustenance from the body itself. On this holiest of days, the body becomes a source of life and nurture rather than its recipient.
Based on an address by the Rebbe, Erev Yom Kippur 5750 (1989) 
1 . Tanya, ch. 2.
2 . See Maimonides' Mishneh Torah, Laws of Repentance 8:2-3; see, however, Rabbi Saadiah Gaon's Emunot V'Dei'ot, sections 47 and 49; Raavad's gloss on Mishneh Torah, ibid.; Nachmanides' Shaar HaGemul (p. 309 in the Chavel edition).
3 . Zohar, part I, 114a; Avodat HaKodesh, 2:41; Shaloh, introduction to Beit David; Likkutei Torah, Tzav 15c and Shabbat Shuvah 65d- 66a; Derech Mitzvotecha, pp. 28-30.
4 . V'kachah 5637, section 88; Yom Tov Shel Rosh Hashanah 5666, p. 528.
Indeed, there are Talmudic and Midrashic passages that imply that there will be eating and drinking in the World to Come (e.g., the "feasts" that G-d will prepare for the righteous). In light of this, the statement that there will be "neither eating nor drinking" might be understood in the sense that the body will not require food or drink for its sustenance, and the consumption of food and drink will be for other purposes (Igrot Kodesh, vol. II, p. 77).
5 . Spiritual entities, such as souls and angels, perceive themselves as vehicles of a divine trait or objective, rather than as beings with an ego and identity of their own, as do physical creatures. (The selflessness of the spiritual is also discernible in consciousless things: a thought or a feeling is always about something else, while a physical object is ostensibly about itself).
6 . Deuteronomy 4:35.
7 . Psalms 33:19; see Likkutei Torah, Shir HaShirim 14b.
8 . Sefer HaSichot 5750, vol. I, p. 30.
(Reprinted from The Week In Review Vol IX No 2)