Excerpt from The Life of St. Antony:

Already in passing I have spoken on these things, and now I must not shrink from speaking on them at greater length, for to put you in remembrance will be a source of safety. Since the Lord visited earth, the enemy is fallen and his powers weakened. Wherefore although he could do nothing, still like a tyrant, he did not bear his fall quietly, but threatened, though his threats were words only. And let each one of you consider this, and he will be able to despise the demons. Now if they were hampered with such bodies as we are, it would be possible for them to say, "Men when they are hidden we cannot find, but whenever we do find them we do them hurt." And we also by lying in concealment could escape them, shutting the doors against them. But if they are not of such a nature as this, but are able to enter in, though the doors be shut, and haunt all the air, both they and their leader the devil, and are wishful for evil and ready to injure; and, as the Saviour said, "From the beginning the devil is a manslayer and a father of vice;" while we, though this is so, are alive, and spend our lives all the more in opposing him; it is plain they are powerless. For place is no hindrance to their plots, nor do they look on us as friends that they should spare us; nor are they lovers of good that they should amend. But on the contrary they are evil, and nothing is so much sought after by them as wounding them that love virtue and fear God. But since they have no power to effect anything, they do nought but threaten. But if they could, they would not hesitate, but forthwith work evil (for all their desire is set on this), and especially against us. Behold now we are gathered together and speak against them, and they know when we advance they grow weak. If therefore they had power they would permit none of us Christians to live, for godliness is an abomination to a sinner. But since they can do nothing they inflict the greater wounds on themselves; for they can fulfil none of their threats. Next this ought to be considered, that we may be in no fear of them: that if they had the power they would not come in crowds, nor fashion displays, nor with change of form would they frame deceits. But it would suffice that one only should come and accomplish that which he was both able and willing to do: especially as every one who has the power neither slays with display nor strikes fear with tumult, but forthwith makes full use of his authority as he wishes. But the demons as they have no power are like actors on the stage changing their shape and frightening children with tumultuous apparition and various forms: from which they ought rather to be despised as shewing their weakness. At least the true angel of the Lord sent against the Assyrian had no need for tumults nor displays from without, nor noises nor rattlings, but in quiet he used his power and forthwith destroyed a hundred and eighty-five thousand. But demons like these, who have no power, try to terrify at least by their displays.