they're magical, they allow magicians to see basic aura/through basic spirit disguises (nat has never had an eye check up and questionable he's gone to any doctor so he could be short-sighted and have no idea)
it's about nat's understanding of violence + demons + the question of responsibility. all of which help feed into his many issues on the concept of violence
nathaniel: yeah, because i didn't ask for the big library
Nathaniel: but that would mean asking you for things
nathaniel: you kill me
arthur:
arthur: no
should feel badneed to learn better logic!!