Everyone knows that you are required to fast on Yom Kippur, but not many people know that there is actually a mitzvah to eat on the day before Yom Kippur. There are many reasons given for this strange mitzvah.
1. Make the fast harder: some say it is to maximize the intensity of the fast by going into the fast on a full stomach.
2. Make the fast easier: others say it is to make the fast easier to make sure that you don't fast two days in a row.
3. Have a festive meal: Yom Kippur is a holiday and therefore requires a meal like all other holidays. Since we fast on the day of, we fulfill the requirement of a yom tov meal the day before.
4. Emphasis: we want to make it clear that we are fasting on Yom Kippur for a mitzvah so therefore we eat the day before to demonstrate that the next day is a fast.
5. To rectify the original sin: The first sin man ever committed was eating from the tree in the garden of Eden. Therefore we have a meal of mitzvah to rectify the original sin of eating for a sin.
6. We're No Angels: Yom Kippur is the one day of the year that we serve God as completely spiritual beings that have no physical needs. On erev Yom Kippur we eat to remind us that the rest of the year we serve God as people of flesh and blood.
7. Last meal: we eat and drink as a last meal like someone who is about to enter judgment.
8. Confidence: We demonstrate that we are not nervous and we know that Hashem will judge us favorably on the day of judgment because He loves us.
I hope everyone eats well today and has a meaningful fast tomorrow. May Hashem inscribe us all into the book of life.