Viduy (confession) is an integral part of the repentance process. It is not enough to feel remorse and forsake sin, although such feelings are a commendable first step. A penitent must put his or her feelings into words and essentially say, "I did such-and-such and for that, I am sorry." Excuses for and rationalizations of the sin are not accepted at this stage of the repentance process. The verbal confession need not necessarily be a confession to another person; confessing alone may allow the penitent to be more honest with him- or herself.
Viduy is slightly different for sins committed against God or one's self than they are for sins committed against another human. Abraham Joshua Heschel once wrote, "According to Jewish tradition, even God Himself can only forgive sins committed against Himself, not against man." True repentance requires the penitent to approach the aggrieved party and correct the sin however possible. Thus, unlike in the repentance in Christianity, the Jewish concept of repentance is not simply the renouncement of sin in general, but rather in the specific sin done against a specific person or group of people. Only then must one go through the introspective processes described above.
Read more about this topic: Repentance In Judaism