Good v. Evil

Many times throughout The Tin Drum, Oskar see's himself as both Jesus and Satan. Oskar mainly describes himself as Satan when he sing-shatters the glass protecting the stores, and allows people to choose between their inner selfishness and selflessness. In a way he is the ultimate judge; he decides who is worthy and who is not. However, when he's instructing the Duster's what to do and how to do it, it's almost as if he's their "creator." He's always watching from afar, never really taking part in what takes place - especially in the church when he disfigures the Madonna and Jesus. He just gets the ball rolling, basically, but he's never in on the action completely.

I feel there could be many different meanings for this, but I'm still somewhat confused as to exactly why he feels he embodies both. Does anyone else have an interpretation for this?