Celsus goes on to say of us: “They set no value on the oracles of the Pythian priestess, of the priests of Dodona, of Clarus, of Branchidæ, of Jupiter Ammon, and of a multitude of others; although under their guidance we may say that colonies were sent forth, and the whole world peopled. But those sayings which were uttered or not uttered in Judea, after the manner of that country, as indeed they are still delivered among the people of Phœnicia and Palestine— these they look upon as marvellous sayings, and unchangeably true.”
In regard to the oracles here enumerated, we reply that it would be possible for us to gather from the writings of Aristotle and the Peripatetic school not a few things to overthrow the authority of the Pythian and the other oracles. From Epicurus also, and his followers, we could quote passages to show that even among the Greeks themselves there were some who utterly discredited the oracles which were recognised and admired throughout the whole of Greece. But let it be granted that the responses delivered by the Pythian and other oracles were not the utterances of false men who pretended to a divine inspiration; and let us see if, after all, we cannot convince any sincere inquirers that there is no necessity to attribute these oracular responses to any divinities, but that, on the other hand, they may be traced to wicked demons— to spirits which are at enmity with the human race, and which in this way wish to hinder the soul from rising upwards, from following the path of virtue, and from returning to God in sincere piety.
It is said of the Pythian priestess, whose oracle seems to have been the most celebrated, that when she sat down at the mouth of the Castalian cave, the prophetic Spirit of Apollo entered her private parts; and when she was filled with it, she gave utterance to responses which are regarded with awe as divine truths. Judge by this whether that spirit does not show its profane and impure nature, by choosing to enter the soul of the prophetess not through the more becoming medium of the bodily pores which are both open and invisible, but by means of what no modest man would ever see or speak of.
And this occurs not once or twice, which would be more permissible, but as often as she was believed to receive inspiration from Apollo. Moreover, it is not the part of a divine spirit to drive the prophetess into such a state of ecstasy and madness that she loses control of herself. For he who is under the influence of the Divine Spirit ought to be the first to receive the beneficial effects; and these ought not to be first enjoyed by the persons who consult the oracle about the concerns of natural or civil life, or for purposes of temporal gain or interest; and, moreover, that should be the time of clearest perception, when a person is in close intercourse with the Deity.
Source: Against Celsus (New Advent)