Rabbi Avishai David teaches the Torah lesson of how the fast of Yom Kippur requires that all of the Jewish People stand unified before G-d. This is the root of the custom to ask our friends for forgiveness before this holy day.
Based on Rabbi Soleveitchik's essay on Kaparah (atonement) and Tahara (purification), in his classic work, Al HaTeshuva. The uniqueness of the teshuva process on Yom Kippur lies within the added dimension of Tahara, when one sincerely repents.