City of Bones
How we cite our quotes:
"Demons, [...] religiously defined as hell's denizens, the servants of Satan, but understood here, for the purposes of the Clave, to be any malevolent spirit whose origin is outside our own home dimension." (1.64)
The Shadowhunters don't seem to know whether demons are the spawn of Satan or not, which goes along with Jace's inner religious conflict. Either way, we don't want to meet any of these demons in a dark alley. Or anywhere. Maybe their religious or non-religious origins are entirely beside the point.
The dreams held her, one after the other, a river of images that bore her along like a leaf tossed in a current. [...] Simon with crosses burned into the palms of his hands. Angels, falling and burning. Falling out of the sky. (5.7)
Clary's not quite sure what it means, but her dream is rich with religious imagery.
"Faeries are fallen angels," said Dorothea, "cast down out of heaven for their pride." (7.55)
Madame Dorothea is sure of herself here, not peppering her beliefs with any "maybes" or "mights." Her mythology is concrete.