Celsus supposes that men “discharge the duties of life until they are loosened from its bonds,” when, in accordance with commonly received customs, they offer sacrifices to each of the gods recognised in the state; and he fails to perceive the true duty which is fulfilled by an earnest piety. For we say that he truly discharges the duties of life who is ever mindful who is his Creator, and what things are agreeable to Him, and who acts in all things so that he may please God. Again, Celsus wishes us to be thankful to these demons, imagining that we owe them thank-offerings.
But we, while recognising the duty of thankfulness, maintain that we show no ingratitude by refusing to give thanks to beings who do us no good, but who rather set themselves against us when we neither sacrifice to them nor worship them. We are much more concerned lest we should be ungrateful to God, who has loaded us with His benefits, whose workmanship we are, who cares for us in whatever condition we may be, and who has given us hopes of things beyond this present life. And we have a symbol of gratitude to God in the bread which we call the Eucharist.
Besides, as we have shown before, the demons have not the control of those things which have been created for our use; we commit no wrong, therefore, when we partake of created things, and yet refuse to offer sacrifices to beings who have no concern with them. Moreover, as we know that it is not demons, but angels, who have been set over the fruits of the earth, and over the birth of animals, it is the latter that we praise and bless, as having been appointed by God over the things needful for our race; yet even to them we will not give the honour which is due to God.
For this would not be pleasing to God, nor would it be any pleasure to the angels themselves to whom these things have been committed. Indeed, they are much more pleased if we refrain from offering sacrifices to them than if we offer them; for they have no desire for the sacrificial odours which rise from the earth.
Source: Against Celsus (New Advent)