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 which is gentle and makes it deeply penitent, and there is a breaking which 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 wo 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.
‘The iron gate that leads into the city’ is a hard heart [Acts 12.10]; but to one who suffers hardship and affliction the gate will open of its own accord, as it did to Peter.
There are many differing methods of prayer. No method is harmful; if it were, it would be not prayer but the activity of Satan.
A man wanted to do evil, but first prayed as usual; and finding himself prevented by God, he was then extremely thankful.
When David wanted to kill Nabal the Carmelite, but was reminded of the divine retribution and abandoned his intention, he was extremely thankful. Again, we know what he did when he forgot God, and how he did not stop until Nathan the Prophet reminded him [cf. 1 Sam 25; 2 Sam 12].
At the times when you remember God, increase your prayers, so that when you forget Him, the Lord may remind you.
St Mark the Ascetic. On the Spiritual Law, 17-25. Philokalia volume 1, pp 111-112