It is absolutely necessary to confess at least once every year.
The longer we go on without confessing, the worse it is for us, the more entangled we become in the bonds of sin, and therefore the more difficult it is to give account. We ought to confess our sins more frequently, in order to strike and scourge the sins by the open avowal of them, and in order to feel a greater loathing of them.
The first motive for sincere confession.
He who is accustomed to give account of his life at confession will not fear to give an answer at the terrible judgment-seat of Christ. For this purpose was the mild tribunal of penitence here instituted, that we may give an answer without shame, having been cleansed and healed through penitence here below.
This is the first motive for sincere confession.
A second motive is inner calm. The more sincerely we confess our sins, the more calm will the soul be afterwards. For sins are secret serpents, gnawing at the heart of a man, and never letting him rest; they are prickly thorns, constantly goring the soul, they are spiritual darkness.
St. John of Kronstadt