Address to the Greeks 16

But the demons who rule over men are not the souls of men; for how should these be capable of action after death? unless man, who while living was void of understanding and power, should be believed when dead to be endowed with more of active power. But neither could this be the case, as we have shown elsewhere. And it is difficult to conceive that the immortal soul, which is impeded by the members of the body, should become more intelligent when it has migrated from it. For the demons, inspired with frenzy against men by reason of their own wickedness, pervert their minds, which already incline downwards, by various deceptive scenic representations, that they may be disabled from rising to the path that leads to heaven. But from us the things which are in the world are not hidden, and the divine is easily apprehended by us if the power that makes souls immortal visits us. The demons are seen also by the men possessed of soul, when, as sometimes, they exhibit themselves to men, either that they may be thought to be something, or as evil-disposed friends may do harm to them as to enemies, or afford occasions of doing them honour to those who resemble them. For, if it were possible, they would without doubt pull down heaven itself with the rest of creation. But now this they can by no means effect, for they have not the power; but they make war by means of the lower matter against the matter that is like themselves. Should any one wish to conquer them, let him repudiate matter. Being armed with the breastplate of the celestial Spirit, he will be able to preserve all that is encompassed by it. There are, indeed, diseases and disturbances of the matter that is in us; but, when such things happen, the demons ascribe the causes of them to themselves, and approach a man whenever disease lays hold of him. Sometimes they themselves disturb the habit of the body by a tempest of folly; but, being smitten by the word of God, they depart in terror, and the sick man is healed.