Just...the significance of Magneto setting up a society where papers are a requirement but Charles, not only is he hidden, but actually does not actually "officially" exist in society, but just in relation to Erik and Raven. He is now essentially an illegal resident in a state Erik set up. It compounds Charles' isolation, dependent on Erik, and reaffirms Erik's possession of him. It's like an agent going undercover and realizing that once his handler's dead, no one will be able to confirm his identity......