For those who fear demons and who think that Satan has any power against the Christian you may find the words of Athanasius that he attributed to Antony, the great ascetic monk, edifying. He wrote:

To end our fear of them, we ought to ponder this: If the capability were theirs, they would not come in great mobs, nor create phantasms, nor would they work their fraud by being transfigured. It would suffice for only one to come and do what he can and wills–especially because everyone who actually possesses the power does not destroy with apparitions, nor arouse fear with large mobs, but exercises his might directly, as he wishes. The demons, however, unable to effect anything, play parts as if they were on stage, changing their forms and striking fear in children by illusion or the hordes and their shapes. For these antics they deserve instead to be ridiculed as weaklings. The true angel of the Lord, at least, who was sent by the Lord to the Assyrians, had no need of hordes, nor of visible apparitions, nor of crashing sounds and rattling noises. He weilded his authority quietly, and at once destroyed a hundred and eighty-five thousand foers. But the demons, who lack the power to do anything, these are the sort who must try to frighten, even if through illusions. [1]

The words of Antony tell us this. Those who fear the demonic do so wrongly. Demons can only scare, manipulate, and deceive. Demons cannot destroy and demons do not have power like we see in the movies (e.g. Constantine). Rather, if demons had any powers there would be no need for spooky antics, but like the angel of the Lord who destoryed the enemies of Israel quickly and quietly, we would all be devistated. Since no such thing happens demons can only threaten, but not act. Christ has conquered the demonic.

[1] Athanasius, The Life of Antony, trans. Robert C. Gregg. New York, NY: Paulist Press, 1980.