St Maximos the Confessor - He, who persuades his conscience to regard the evil...

He, who persuades his conscience to regard the evil he is doing as good by nature, reaches out with his moral faculty as with a hand and grasps the tree of life in a reprehensible manner; for he thinks that what is thoroughly evil is by nature immortal.

Therefore God, who has implanted in man’s conscience a natural hatred of evil, cuts him off from life, for he has now become evil in his will and intention.

God acts in this way so that when a man does wrong he cannot persuade his own conscience that what is thoroughly evil is good by nature.

St Maximos the Confessor