On The Holy Trinity by St. Augustine
Chapter 11.--Miracles Which are Done by Demons are to Be Spurned.
14. For it is easy for the most worthless spirits to do many things by means of aerial bodies, such as to cause wonder to souls which are weighed down by earthly bodies, even though they be of the better inclined. For if earthly bodies themselves, when trained by a certain skill and practice, exhibit to men so great marvels in theatrical spectacles, that they who never saw such things scarcely believe them when told; why should it be hard for the devil and his angels to make out of corporeal elements, through their own aerial bodies, things at which the flesh marvels; or even by hidden inspirations to contrive fantastic appearances to the deluding of men's senses, whereby to deceive them, whether awake or asleep, or to drive them into frenzy? But just as it may happen that one who is better than they in life and character may gaze at the most worthless of men, either walking on a rope, or doing by various motions of the body many things difficult of belief, and yet he may not at all desire to do such things, nor think those men on that account to be preferred to himself; so the faithful and pious soul, not only if it sees, but even if on account of the frailty of the flesh it shudders at, the miracles of demons; yet will not for that either deplore its own want of power to do such things, or judge them on this account to be better than itself; especially since it is in the company of the holy, who, whether they are men or good angels, accomplish, through the power of God, to whom all things are subject, wonders which are far greater and the very reverse of deceptive.