The answer is hinted at in that ubiquitous symbol of Rosh Hashanah – the apple dipped in honey. Apple and honey represent a harmonious interaction between substances of two different origins. And different they are! The apple is an example of a direct creation of God – it signifies nature without interference. Honey is a processed food. Nature supplied the ingredients (the flower, the nectar, the bee, the hive, the honeycomb), but left to its own devices, these components on their own would not have metamorphosed into honey. That required intervention. Rabbi David Lapin calls the apple in honey symbolic of the harmony of nature and industry.

But apple in honey symbolizes only a harmonious interaction, not a fusion. The apple remains an apple and the honey remains honey. They simply enhance one another. Nature remains nature and industry remains industry. They do not merge and become one. It is the symbol of Rosh Hashanah, but Yom Kippur represents a different idea.

On Yom Kippur, the Kohen Gadol enters the inner sanctum of God’s dwelling place on earth. The intimacy of that encounter suggests a merging of two similarly different entities – the human and the Divine. For one brief moment on that one special day, the High Priest brings all mankind with him into the Holy of Holies by way of his spirit, and the barriers that typically block the connection between the human and the Divine temporarily vanish. All the confessions of the day now make sense as well – they are the last-minute housecleaning of our sullied souls, clearing the way for a more perfect union with the untarnished nature of Divinity.

This explains why we must fast on Yom Kippur. If atonement is the necessary outcome of the fusion of God and man, fasting is its necessary accompaniment. Fasting on Yom Kippur enables the fusion of two other entities otherwise in combative conflict – the body and the soul. The body does not simply “get along” with the spirit on Yom Kippur (as, perhaps, it may be said to do on a standard Shabbat). On Yom Kippur, the body is subsumed within the spirit, its normal needs sublimated by the contentment of the soul. The two merge and become one. We still have bodies, but they are now angel-like, clothed in white, standing in motionless devotion, in need of no material nourishment whatsoever. With bodies like these, we are able to become one with the body of the Kohen Gadol, and he is able to fuse with the Shechina.

Fasting does not weaken our ability to perform the avodah of Yom Kippur. On the contrary, it is the act of fasting that enables the avodah of Yom Kippur.