Celsus afterwards states what is adduced by Jews and Christians alike in defence of abstinence from idol sacrifices, namely, that it is wrong for those who have dedicated themselves to the Most High God to eat with demons. What he brings forward against this view, we have already seen. In our opinion, a man can only be said to eat and drink with demons when he eats the flesh of what are called sacred victims, and when he drinks the wine poured out to the honour of the demons. But Celsus thinks that we cannot eat bread or drink wine in any way whatever, or taste fruits, or even take a draught of water, without eating and drinking with demons.
He adds also, that the air which we breathe is received from demons, and that not an animal can breathe without receiving the air from the demons who are set over the air. If any one wishes to defend this statement of Celsus, let him show that it is not the divine angels of god, but demons, the whole race of whom are bad, that have been appointed to communicate all those blessings which have been mentioned. We indeed also maintain with regard not only to the fruits of the earth, but to every flowing stream and every breath of air that the ground brings forth those things which are said to grow up naturally,— that the water springs in fountains, and refreshes the earth with running streams—that the air is kept pure, and supports the life of those who breathe it, only in consequence of the agency and control of certain beings whom we may call invisible husbandmen and guardians; but we deny that those invisible agents are demons.
And if we might speak boldly, we would say that if demons have any share at all in these things, to them belong famine, blasting of the vine and fruit trees, pestilence among men and beasts: all these are the proper occupations of demons, who in the capacity of public executioners receive power at certain times to carry out the divine judgments, for the restoration of those who have plunged headlong into wickedness, or for the trial and discipline of the souls of the wise. For those who through all their afflictions preserve their piety pure and unimpaired, show their true character to all spectators, whether visible or invisible, who behold them; while those who are otherwise minded, yet conceal their wickedness, when they have their true character exposed by misfortunes, become manifest to themselves as well as to those whom we may also call spectators.
Source: Against Celsus (New Advent)