RAV KOOK EMOR Part 1 Eating before Yom Kippur

The Ninth of Tishrei While there are several rabbinically-ordained fasts throughout the year, only one day of fasting is mentioned in the Torah: "It is a sabbath of sabbaths to you, when you must fast. You must observe this sabbath on the ninth of the month in the evening, from evening until [the next] evening." (Lev. 23:32) This refers to the fast of Yom Kippur. The verse, however, appears to contain a rather blatant 'mistake': Yom Kippur falls out on the tenth of Tishrei, not the ninth! The Talmud in Berachot 8b explains that the day before Yom Kippur is also part of the atonement process, even though there is no fasting: "This teaches that one who eats and drinks on the ninth is credited as if he fasted on both the ninth and tenth." Still, we need to understand: Why is there a mitzvah to eat on the day before Yom Kippur? In what way does this eating count as a day of fasting?