Excerpt from The Life of St. Antony:

'And let us strive that wrath rule us not nor lust overcome us, for it is written, "The wrath of man worketh not the righteousness of God. And lust, when it hath conceived, beareth sin, and the sin when it is full grown bringeth forth death.'' Thus living, let us keep guard carefully, and as it is written, "keep our hearts with all watchfulness." For we have terrible and crafty foes--the evil spirits--and against them we wrestle, as the Apostle said," Not against flesh and blood, but against the principalities and against the powers, against the world-rulers of this darkness, against the spiritual hosts of wickedness in the heavenly places." Great is their number in the air around us", and they are not far from us. Now there are great distinctions among them; and concerning their nature and distinctions much could be said, but such a description is for others of greater powers than we possess. But at this time it is pressing and necessary for us only to know their wiles against ourselves.