The Psalmist bears witness that divine justice employs certain evil angels to inflict calamities upon men: “He cast upon them the fierceness of His anger, wrath, and indignation, and trouble, sent by evil angels.” Whether demons ever go beyond this when they are suffered to do what they are ever ready, though through the restraint put upon them they are not always able to do, is a question to be solved by that man who can conceive, in so far as human nature will allow, how it accords with the divine justice, that such multitudes of human souls are separated from the body while walking in the paths which lead to certain death.
“For the judgments of God are so great,” that a soul which is still clothed with a mortal body cannot comprehend them; “and they cannot be expressed: therefore by unnurtured souls” they are not in any measure to be understood. And hence, too, rash spirits, by their ignorance in these matters, and by recklessly setting themselves against the Divine Being, multiply impious objections against providence. It is not from demons, then, that men receive any of those things which meet the necessities of life, and least of all ourselves, who have been taught to make a proper use of these things.
And they who partake of grain and wine, and the fruits of trees, of water and of air, do not feed with demons, but rather do they feast with divine angels, who are appointed for this purpose, and who are as it were invited to the table of the pious man, who hearkens to the precept of the word, which says, “Whether you eat or drink, or whatever you do, do all to the glory of God.” And again, in another place it is written, “Do all things in the name of God.” When, therefore, we eat and drink and breathe to the glory of God, and act in all things according to what is right, we feast with no demons, but with divine angels: “For every creature is good, and nothing to be refused, if it be received with thanksgiving: for it is sanctified by the word of God and prayer.” But it could not be good, and it could not be sanctified, if these things were, as Celsus supposes, entrusted to the charge of demons.
Source: Against Celsus (New Advent)