Yom Kippur is an aweome day of return: returning to healthy relationships with others, and returning to the real, pure spiritual essence of who we are. And what makes that possible is both the forgiveness that Hashem (and other people!) lovingly grants us,and the PURIFICATION that we experience. All the "stains" on our souls, so to speak (from the hurtful and negative words, deeds and thoughts we all--as human beings--fell into), are utterly washed away. We are purified through the observances of Yom Kippur, as we are purified by the waters of a holy mikveh! And it gets out EVEN the coffee stains!