Shavua Tov. Moadim Lesimcha. Rabbi J.B. Soloveitchik זצ״ל makes an interesting observation about Yom Kippur and the first day of creation. When the Torah says ויהי ערב ויהי בוקר יום אחד, the יום אחד, the "one day" refers to that one special day known as Yom Kippur.
The idea here is that ערב, or night, is a time of ערבוביה, or confusion. It also represents how darkness and hopelessness might infiltrate an individual. The Midrash makes this connection between יום אחד and Yom Kippur to say that without this special day, the world would not has been created.
This one day a year of renewal and reflection and connection to G-d is necessary to give the feeling of a new start. There is light after the darkness and there is always hope. The spark of the Divine in man is inextinguishable.