Midrash Rabbah teaches us that Yom Echad refers to Yom Kippuras the quintessential day when man recognizes his sin and returns to Hashem from the innermost recesses of his soul and the depth of sin. Yom Kippur requires man display both Erev and Boker aspects of repentance. On the night of Yom Kippur, man grabs his head and says, “I have been so confused, what have I done?” He must be overcome with the anguish and embarrassment of his sin while feeling engulfed by confusion. This is the repentance of Erev, evening and night of Yom Kippur. Only then can he clearly atone for his sins though the repentance of Boker, by wrapping himself in the various parts of repentance, including forsaking the sin completely (azivas hachet), admission of guilty actions (viduy) and acceptance upon himself not to return to this sin in the future (kabbalah l’habah).
Gmar chasimah tovah.