After all that we have already said concerning Jesus, it would be a useless repetition for us to answer these words of Celsus: “It is easy to convict them of worshipping not a god, not even demons, but a dead person.” Leaving, then, this objection for the reason assigned, let us pass on to what follows: “In the first place, I would ask why we are not to serve demons? Is it not true that all things are ordered according to God's will, and that His providence governs all things?
Is not everything which happens in the universe, whether it be the work of God, of angels, of other demons, or of heroes, regulated by the law of the Most High God? Have these not had assigned them various departments of which they were severally deemed worthy? Is it not just, therefore, that he who worships God should serve those also to whom God has assigned such power? Yet it is impossible, he says, for a man to serve many masters.” Observe here again how he settles at once a number of questions which require considerable research, and a profound acquaintance with what is most mysterious in the government of the universe.
For we must inquire into the meaning of the statement, that “all things are ordered according to God's will,” and ascertain whether sins are or are not included among the things which God orders. For if God's government extends to sins not only in men, but also in demons and in any other spiritual beings who are capable of sin, it is for those who speak in this manner to see how inconvenient is the expression that “all things are ordered by the will of God.” For it follows from it that all sins and all their consequences are ordered by the will of God, which is a different thing from saying that they come to pass with God's permission.
For if we take the word “ordered” in its proper signification, and say that “all the results of sin were ordered,” then it is evident that all things are ordered according to God's will, and that all, therefore, who do evil do not offend against His government. And the same distinction holds in regard to “providence.” When we say that “the providence of God regulates all things,” we utter a great truth if we attribute to that providence nothing but what is just and right. But if we ascribe to the providence of God all things whatsoever, however unjust they may be, then it is no longer true that the providence of God regulates all things, unless we refer directly to God's providence things which flow as results from His arrangements.
Celsus maintains also, that “whatever happens in the universe, whether it be the work of God, of angels, of other demons, or of heroes, is regulated by the law of the Most High God.” But this also is incorrect; for we cannot say that transgressors follow the law of God when they transgress; and Scripture declares that it is not only wicked men who are transgressors, but also wicked demons and wicked angels.
Source: Against Celsus (New Advent)