According to Elaine Pagels this is one of his arguments:
What makes the Christians' message dangerous, Celsus writes, is not that they believe in one God, but that they deviate from monotheism by their "blasphemous" belief in the devil. For all the "impious errors" the Christians commit, Celsus says, they show their greatest ignorance in "making up a being opposed to God, and calling him 'devil' or, in the Hebrew language, 'Satan.' All such ideas, Celsus declares, are nothing but human inventions, sacrilegious even to repeat: "it is blasphemy... to say that the greatest God... has an adversary who constrains his capacity to do good." Celsus is outraged that the Christians, who claim to worship one God, "impiously divide the kingdom of God creating rebellion in it, as if there were opposing factions within the divine, including one that is hostile to God!
Celsus accuses Christians of "inventing a rebellion" (meaning sedition) in heaven to justify rebellion here on earth.He has other objections too, but today I thought I'd put this one up to consider.
As it turns out, quite a few people thought (and still think) about this division and the ludicrous notion that God has an antagonistic also divine being fighting him, perhaps an equal. If God created all, and God is all good, then how can this be accurate? It does not make sense. In the creation stories, God saw that all was "good."
I invite us to think about this. It has been a very long time since I believed in satan. I arrived at that conclusion on my own. And, I find Celsus' argument very interesting.