Impurity is permitted in the context of the community -- the case of a kohen offering the omer korban, and it becomes impure. What to do if there is no other pure offering to replace the impure one? Which leads to a discussion about the status of Impurity. Also, the tzitz, that sits on the kohen gadol's forehead (and if not there, it doesn't have the power that it does when worn, or depending on the debate about it). Relevant also to the kohen gadol's personal worship. So... Is the tzitz what's important, or the kohen wearing it?