“A man or a woman who sins… let them confess their sins.” (Bemidbar 5:6-7)
One is required to repent and confess his sins, to feel regret and shame over his wrongdoings, and to commit himself to improve his ways. This mitzvah applies all year, but Yom Kippur is our last chance before the final judgment of the year.
By verbally admitting that we have sinned, we are acknowledging that
1. We understand that Hashem knows everything we do;
2. We are sincere in our regret; and
3. We will try harder next time to refrain from this sin.
Thus, Hashem will forgive us and help us to improve (Sefer HaChinuch, mitzvah 364).
Text Copyright © 2008 by Rabbi Moshe Goldberger and Torah.org.