Yom Kippur is a day of Teshuvah for all-even the non-sinners:
Every Jew is required to perform Teshuvah, even one who has never sinned. Even the righteous must arouse mercy on the decent of their soul that has entered impurity. It is on this form of Teshuvah that the coming of Moshiach is dependent.
 Likkutei Torah Ki Seitzei last Mamar