Responding to these authorities, we say that the authority A good tree, etc. (Matth. 7) is to be understood of a good or evil intention: for from a good intention proceeds only a good work, and from an evil intention only an evil one. We also say that this word "evil" sometimes signifies an evil action, sometimes the deformity of that action; as when it is said: There is no evil in the city which God has not done — that is, there is no evil action which he does not allow to happen; but the malice itself, that is, the deformity of the action, according to which it is called evil, is nothing, nor does he himself cause it. For the deformity of the action, by which the action is called evil, is nothing. Insofar, then, as this word signifies an evil action, evil is said to be something, and to be from God — not in that it is evil, but in that it is. But insofar as it signifies malice, it is said to be neither something, nor from God; for it denotes rather a privation of being than a positing of a thing. We also say that this word "darkness" denotes rather the absence of light than the existence of a thing, and therefore the world did not have its beginning from darkness. But the sense is: Darkness was upon the face of the deep (Gen. 1), that is, there was no light. Nor is the devil called the prince of the world because he created the world, but prince of the world, that is, of worldly men, because he rules in their hearts, and reigns through earthly desire. By the same reasoning he is called lord of the world. That "the world" means "lovers of the world" is read in John, where it is said: And the world knew him not (John 1), that is, the lovers of the world. And elsewhere in the Gospel: My kingdom is not of this world (John 18); that is, the lovers of this world are not my kingdom; that is, I do not reign in them. The devil, moreover, is called father of men not by reason of creation, but by reason of imitation, because through wicked deeds men imitate him. Sin, moreover, is said to dwell in the flesh of man — that is, the kindling of sin, or concupiscence — which dwells in the flesh not by reason of substance, but by reason of circumstance. For from the time Adam sinned, the flesh was made prone to desire, that is, man became weak in the flesh. Although, then, concupiscence remains in the flesh occasionally, the flesh is not therefore evil — that is, vicious — but vitiated, or weakened; nor is it therefore any less from God. Just as man, although he is weak, nevertheless has his existence from God.
In similar fashion the following authority is explained; for although the law of sin and death, that is concupiscence, arises in and from the members occasionally — that is, from the weakness of the members — nevertheless those members, although vitiated, are, insofar as they exist, from God; but as vitiated, that is, weakened, they are not from God.
That the flesh is said to fight against the spirit is not to be understood of the flesh itself, but of the carnality of the flesh: for the flesh, that is, carnality, always contradicts the spirit, that is, reason.