Our exposure to sin can coarsen our hearts over time and we can become insensitive to the pleas of Divine Love. The fathers teach that the heart, therefore, must be broken. It must be shattered, but not in a violent fashion. Rather, it is through prayer, especially through vigils - when the mind and body have been humbled - that true compunction emerges. The heart is shattered through the knowledge of one's sins in the face of the love of God and His desire for the soul. This sorrow opens the door to the heart.
“To brood on evil makes the heart brazen; but to destroy evil through self-restraint and hope breaks the heart. There is a breaking of the heart that is gentle and makes it deeply penitent, and there is a breaking that is violent and harmful, shattering it completely. Vigils, prayer, and patient acceptance of what comes constitute a breaking that does not harm but benefits the heart, provided we do not destroy the balance between them through excess. He who perseveres in them will be helped in other ways as well; but he who is slack and negligent will suffer intolerably on leaving this life. A self-indulgent heart becomes a prison and chain for the soul when it leaves this life; whereas an assiduous heart is an open door.
St. Mark the Ascetic”