Eating on Erev Yom Kippur

Rabbeinu Yonah, Shaarei Teshuva 4:8
The Gemara (Rosh Hashana 9a) says whoever has a set meal on Erev Yom Kippur is as if he was commanded to fast on the ninth and tenth [of Tishrei] and he did, because he shows his excitement at the arrival of the day of his atonement, and it testifies his worry for his guilt and his sorrow for his sins.

[9] The second reasonis on holidays we have a meal for the happiness of the mitzvah...but because we must fast on Yom Kippur, we are obligated to have the meal on Erev Yom Kippur.

[10] And the third reason is to strengthen ourselves to be able to say the many prayers and supplications on Yom Kippur and to be able to make personal resolutions about Teshuva.