User blog comment:Darchangel 66/Castiel (Jimmy) as Lucifers vessel/@comment-27270979-20160121030957/@comment-31283382-20160123113934

Guys, before anything, just remember Anael (or Anna, if you will). After she Fell, her human body was owned by her now human soul. After she regained her grace, her human body was at the very least atomized, but she was still able to somehow reasemble it and enter it. How?

Simple; the Anna Milton was erased, leaving behind only Anael. While it is true that the body she had was her, the body was also just that-a body. She basically forged for herself an object that never had a soul to begin with and managed to bind herself to it.

Castiel and Jimmy both died when Raphael broke their physical container down into atoms. However, Jimmy proceded to the afterlife, and his body, now soulles and atomized, was rebuilt into a soulles, unsentinent object that was given to Castiel for usage. Due to that, this was no longer Jimmy's body, but Castiel's. His Grace was the only soul essence inside of a body, making it his actuall body, and not a vessel. It's also possible that this means that he is immune to exorcism.