The Vidui is the climactic section of each of the five Yom Kippur services when, bent over and contrite, we beat our breasts and enumerate the ways we have fallen short of the mark in the previous year. According to many, Vidui is the actualisation of teshuvah, repentance (Maimonides, Laws of Repentance 1:1). The Torah does not clearly command repentance, but it does command Vidui (Numbers 5:6-7).
Our hearts may be filled with feelings of remorse and resolutions for self-improvement. But these emotions usually jostle with excuses and self-justifications. When we can articulate out loud, I have sinned, I have done a,b,c the chaotic feelings of regret crystallise into sincere resolve.
Vidui is usually translated as confession, but this carries misleading connotations of self-abasement from other religions, and conveys no sense of the root meaning of the Hebrew word. Vidui in origin means to thank, praise or, most accurately in our context, to acknowledge.
The Vidui bikkurim is a declaration of thanksgiving to God when we bring the first fruits of the Land of Israel to Jerusalem (Deuteronomy 26:1-11).
In the Vidui of Yom Kippur, we peel off our customary layers of denial and rationalisation to admit that we have not been who we could and should have been. In this vein, a Chasidic Rebbe said that we should not smite our hearts punitively in the Vidui, but rather knock gently upon them so that they may open up to acknowledge the truth.