Because the service of the day is a Divinely granted means of gaining purity, even the preparation for the day assumes a unique nature. Meiri (Essay on Teshuvah) comments that the precept to eat on the eve of Yom Kippur is designed to free the body on Yom Kippur so that it need not expend energy on anything save the service of G-d.
Thus, because the enjoyment of food and drink on the day before Yom Kippur is a device to make possible the successful assault on a spiritual summit on Yom Kippur, even the eating and drinking are tantamount to the fasting and solemn service of Yom Kippur itself. As the Sages teach: Whoever eats and drinks on the ninth (day of Tishrei, the eve of Yom Kippur) is considered as if he had fasted on the ninth and tenth (Tr. Yoma 86a). The dedication of the ninth day elevates even the eating to the level of a spiritual experience.
printed in Arachim Newsletter about 20 years agao from Artscroll by Rabbi Nosson Scherman