He adds, “And indeed he who, when speaking of God, asserts that there is only one who may be called Lord, speaks impiously, for he divides the kingdom of God, and raises a sedition therein, implying that there are separate factions in the divine kingdom, and that there exists one who is His enemy.” He might speak after this fashion, if he could prove by conclusive arguments that those who are worshipped as gods by the heathens are truly gods, and not merely evil spirits, which are supposed to haunt statues and temples and altars.
But we desire not only to understand the nature of that divine kingdom of which we are continually speaking and writing, but also ourselves to be of those who are under the rule of God alone, so that the kingdom of God may be ours. Celsus, however, who teaches us to worship many gods, ought in consistency not to speak of “the kingdom of God,” but of “the kingdom of the gods.” There are therefore no factions in the kingdom of God, nor is there any god who is an adversary to Him, although there are some who, like the Giants and Titans, in their wickedness wish to contend with God in company with Celsus, and those who declare war against Him who has by innumerable proofs established the claims of Jesus, and against Him who, as the Word, did, for the salvation of our race, show Himself before all the world in such a form as each was able to receive Him.
Source: Against Celsus (New Advent)