Mosiah 26-28

Quote "You always need to confess your sins to the Lord. If they are serious transgressions, such as immorality, they need to be confessed to a bishop or stake president. Please understand that confession is not repentance. It is an essential step, but is not itself adequate. Partial confession by mentioning lesser mistakes will not help you resolve a more serious, undisclosed transgression. Essential to forgiveness is a willingness to fully disclose to the Lord and, where necessary, His priesthood judge all that you have done."

~Elder Richard G. Scott

Question "Why is confession an essential part of repentance?"

Confession is a very important part of repentance because it means that you are humbling yourself to be subject to judgement....that's not easy for anyone. Even if you know what the punishment will be, it is not an easy thing to say "I messed up, and here's what I did, even though I know it was wrong". You can't have a truly repentant attitude, and not be willing to openly admit that you made a mistake, or committed a sin.

The Lord already knows what we think, feel, and do every second of every day....He doesn't need us to tell Him, however, when we humble ourselves, and acknowledge our sins, through prayer, it is an opportunity for us to exercise faith in Him, that He loves us enough to forgive us our sins. Saying that you're sorry always makes you feel better, and so it is with repentance. The whole process of repentance is recognizing how bad you feel for breaking a commandment, and feeling unworthy to receive blessings, acknowledging or confessing that you broke a commandment, then apologizing for breaking that commandment, and trying your best not to do it again, and finally accepting any consequence of that decision. All of these elements are important to the repentance process.