Never suffer sin to remain upon you; let it not grow old in you; wipe it off while it is fresh, else it will stain; let it not get ingrained; let it not eat its way in, and rust in you. It is of a consuming nature; it is like a canker; it will eat your flesh. I say, beware, my brethren, of suffering sin in yourselves, and this for a great many reasons. First, if for no other than this, you will forget you have committed it, and never repent of it at all. Repent of it while you know it; let it not be wiped from your memory without being first wiped away from your soul. What may be the state of our souls from the accumulating arrears of the past! Alas! what difficulties we have involved ourselves in, without knowing it.
--Blessed John Henry Newman, “Transgressions and Infirmities”, Parochial and Plain Sermons, Vol. 5