Celsus, indeed, evinced a slight knowledge of Scripture when he made Jesus say, that it is “a certain Satan who contrives such devices;” although he begs the question when he asserts that “Jesus did not deny that these works have in them nothing of divinity, but proceed from wicked men,” for he makes things which differ in kind to be the same. Now, as a wolf is not of the same species as a dog, although it may appear to have some resemblance in the figure of its body and in its voice, nor a common wood-pigeon the same as a dove, so there is no resemblance between what is done by the power of God and what is the effect of sorcery.
And we might further say, in answer to the calumnies of Celsus, Are those to be regarded as miracles which are wrought through sorcery by wicked demons, but those not which are performed by a nature that is holy and divine? And does human life endure the worse, but never receive the better? Now it appears to me that we must lay it down as a general principle, that as, wherever anything that is evil would make itself to be of the same nature with the good, there must by all means be something that is good opposed to the evil; so also, in opposition to those things which are brought about by sorcery, there must also of necessity be some things in human life which are the result of divine power.
And it follows from the same, that we must either annihilate both, and assert that neither exists, or, assuming the one, and particularly the evil, admit also the reality of the good. Now, if one were to lay it down that works are wrought by means of sorcery, but would not grant that there are also works which are the product of divine power, he would seem to me to resemble him who should admit the existence of sophisms and plausible arguments, which have the appearance of establishing the truth, although really undermining it, while denying that truth had anywhere a home among men, or a dialectic which differed from sophistry.
But if we once admit that it is consistent with the existence of magic and sorcery (which derive their power from evil demons, who are spell-bound by elaborate incantations, and become subject to sorcerers) that some works must be found among men which proceed from a power that is divine, why shall we not test those who profess to perform them by their lives and morals, and the consequences of their miracles, viz., whether they tend to the injury of men or to the reformation of conduct?
What minister of evil demons, e.g., can do such things? And by means of what incantations and magic arts? And who, on the other hand, is it that, having his soul and his spirit, and I imagine also his body, in a pure and holy state, receives a divine spirit, and performs such works in order to benefit men, and to lead them to believe in the true God? But if we must once investigate (without being carried away by the miracles themselves) who it is that performs them by help of a good, and who by help of an evil power, so that we may neither slander all without discrimination, nor yet admire and accept all as divine, will it not be manifest, from what occurred in the times of Moses and Jesus, when entire nations were established in consequence of their miracles, that these men wrought by means of divine power what they are recorded to have performed?
For wickedness and sorcery would not have led a whole nation to rise not only above idols and images erected by men, but also above all created things, and to ascend to the uncreated origin of the God of the universe.
Source: Against Celsus (New Advent)