Seeking God, then, in this way, we have no need to visit the oracles of Trophonius, of Amphiaraus, and of Mopsus, to which Celsus would send us, assuring us that we would there “see the gods in human form, appearing to us with all distinctness, and without illusion.” For we know that these are demons, feeding on the blood, and smoke, and odour of victims, and shut up by their base desires in prisons, which the Greeks call temples of the gods, but which we know are only the dwellings of deceitful demons.
To this Celsus maliciously adds, in regard to these gods which, according to him, are in human form, “they do not show themselves for once, or at intervals, like him who has deceived men, but they are ever open to intercourse with those who desire it.” From this remark, it would seem that Celsus supposes that the appearance of Christ to His disciples after His resurrection was like that of a spectre flitting before their eyes; whereas these gods, as he calls them, in human shape always present themselves to those who desire it.
But how is it possible that a phantom which, as he describes it, flew past to deceive the beholders, could produce such effects after it had passed away, and could so turn the hearts of men as to lead them to regulate their actions according to the will of God, as in view of being hereafter judged by Him? And how could a phantom drive away demons, and show other indisputable evidences of power, and that not in any one place, like these so-called gods in human form, but making its divine power felt through the whole world, in drawing and congregating together all who are found disposed to lead a good and noble life?
Source: Against Celsus (New Advent)