The Rambam in Hilchos T’shuvah, The Laws of Repentance, based on the Gemara in Rosh HaShanah (17b) and Yoma (85b), famously rules that Yom Kippur is only for the cleansing of those sins that are between man and G-d; but those between man and his fellow man can only be forgiven if the antagonist receives forgiveness from the aggrieved partner. Rav Tzvi Hirsch Chajes, early 19th century commentator on the Talmud, explains that with sins between man and G-d, Hashem is the litigant; and as a “victim,” He is in a position to forgive. But with sins between man and fellow man, Hashem is the judge and He needs to weigh who is the correct party between the two disputants. Until one comes clean, admits guilt, and apologizes, a favorable judgment cannot be rendered.