No man can conquer the passions except by the palpable virtues; and no man can conquer the wandering of the mind except by the study of spiritual knowledge. Our mind is light and swift, and if it is not tied down by some reflection, it never stops wandering. Without attaining perfection in the aforesaid virtues, a man cannot acquire this safeguard. For if a man does not vanquish his enemies, he cannot be at peace.
Homily 34 (p. 283).