Why confess your sins?

[Flavio Raposo]

Go to your confessor; open your heart to him; display to him all the recesses of your soul; take the advice that he will give you with the utmost humility and simplicity. For God, Who has an infinite love for obedience, frequently renders profitable the counsels we take from others, but especially from those who are the guides of our souls.
--St. Francis de Sales

A humble confession displeases Satan and, if he could, he would make you omit Holy Communion.
--Imitation of Christ

Three conditions are necessary for Penance: contrition, which is sorrow for sin, together with a purpose of amendment; confession of sins without any omission; and satisfaction by means of good works.
--St. Thomas Aquinas

Confession heals, confession justifies, confession grants pardon of sin, all hope consists in confession; in confession there is a chance for mercy.
--St. Isidore of Seville