131:3 It is a mitzvah to eat and drink extra at the meal before Yom Kippur. If one eats and drinks on the day before Yom Kippur for the sake of this mitzvah, it is considered as if he had fasted on that day as well. (There’s even reason to learn less Torah that day in order to have more time to eat – Mishnah Brurah 604:1.) It is a mitzvah to eat fish as part of the first meal of the day.
131:4 Yom Kippur does not atone for sins a person has committed against his fellow man until he has appeased the injured party, as per Leviticus 16:30, “from all your sins before Hashem, you will be cleansed.” That is to say that Yom Kippur only atones for sins that are before Hashem. Whatever is between a person and his fellow man, Yom Kippur will not atone until he appeases that person. Therefore, a person must be diligent that if he is in unlawful possession of someone else’s money, he must return it and rectify things. (If one has stolen property or similar things that must be returned, he may not wait until erev Yom Kippur to return it – Shaar HaTziyon 606:2.) If he is in possession of money and he is not sure about whether or not it rightfully belongs to him, he should notify the other person that he wants to go to beis din with him immediately after Yom Kippur. He must sincerely resolve to act according to whatever the court decides.
If one wronged another person verbally, he must appease him. A person is obligated to go to the injured party to apologize. If this is too difficult, or if he realizes that his apology will be more readily accepted through a third party, then he may send someone else. The one being apologized to should forgive him sincerely and not be cruel, since that is not a trait of Jews. Rather, it is a trait of Esau, about whom the book of Amos (1:11) says, “His wrath is preserved forever.” Similarly, it is a trait of the Gibonites, who would not forgive or be appeased (II Samuel 21:2). The trait of the Jews is to be slow to anger and easy to pacify. When the offending party asks for forgiveness, one should forgive him sincerely and willingly. Even if he caused him much pain, he should not seek revenge or bear a grudge. Just the opposite: if the one who wronged him does come to ask forgiveness, the injured party should make himself accessible to facilitate the offender asking his forgiveness. If one does not overcome his hatred by Yom Kippur, his prayers will not be heard, G-d forbid. If one rises above this inclination, all his sins will be forgiven.