Even Porphyry asserts that it was revealed by divine oracles that we are not purified by any sacrifices to sun or moon, meaning it to be inferred that we are not purified by sacrificing to any gods. For what mysteries can purify, if those of the sun and moon, which are esteemed the chief of the celestial gods, do not purify? He says, too, in the same place, that "principles" can purify, lest it should be supposed, from his saying that sacrificing to the sun and moon cannot purify, that sacrificing to some other of the host of gods might do so. And what he as a Platonist means by "principles," we know. For he speaks of God the Father and God the Son, whom he calls (writing in Greek) the intellect or mind of the Father; but of the Holy Spirit he says either nothing, or nothing plainly, for I do not understand what other he speaks of as holding the middle place between these two. For if, like Plotinus in his discussion regarding the three principal substances, he wished us to understand by this third the soul of nature, he would certainly not have given it the middle place between these two, that is, between the Father and the Son. For Plotinus places the soul of nature after the intellect of the Father, while Porphyry, making it the mean, does not place it after, but between the others. No doubt he spoke according to his light, or as he thought expedient; but we assert that the Holy Spirit is the Spirit not of the Father only, nor of the Son only, but of both. For philosophers speak as they have a mind to, and in the most difficult matters do not scruple to offend religious ears; but we are bound to speak according to a certain rule, lest freedom of speech beget impiety of opinion about the matters themselves of which we speak.