Demons wage war against the soul primarily through thoughts, not through things; for things fight against us in their own right. Hearing and sight are responsible for the warfare waged through things, habit and demons for that waged through thoughts.
The body cannot be purified without fasting and vigil, the soul without mercy and truth, and the intellect without contemplation of God and communion with Him. These pairs constitute the principal virtues in these three aspects of the human person.
When the soul moves in obedience to these virtues, her citadel–patient endurance–is not disturbed by temptations. ‘You will gain possession of your souls through your patient endurance’ (Luke 21:19), says the Logos. Otherwise the soul will be shaken by fits of cowardice, as an unwalled city is by a distant uproar.
~Ilias the Presbyter