EXAMPLES:
On pride by St. Anthony of Optina
Wherever we may decide to withdraw or settle, we will drag along out inner chaos; for just as everywhere is an earthly paradise to the humble soul, everywhere will be torture and hard labor to the proud.
On evil by St. Paisios the Athonite
The devil has neither power nor dominion over those who have faith, go to church regularly, and receive Holy Communion. He just barks a little - 'arf, arf!' - like a dog without teeth. But he has great power over one who has no faith and gives him the excuse to take over. He can lynch him and tear him to pieces with his teeth. The devil's authority on a soul depends on the rights this soul has granted him.
On prayer by St. Agathon of Egypt
I think there is no greater labor than that of prayer to God. For every time a man wants to pray, his enemies, the demons, want to prevent him, for they know that it is only by turning him from prayer that they can hinder his journey. Whatever good work a man undertakes, if he perseveres in it, he will attain rest. But prayer is warfare to the last breath.
On humility by St. Isaac the Syrian
The only way that a man who wishes to be wise in the eyes of God can do so is to become a fool to the world and a despiser of human glory. Awesome is the man who conceals the greatness of his labour by self-reproach; at such a man the angels marvel.