They see his ideas of what's inside the law as rather childish, and suppose he's afraid himself of what he wants to make the man frightened of. Yes, he's more afraid of it than the man, as the man wants nothing but to go inside the law, even after he's heard about the terrible doormen there, in contrast to the doorkeeper who doesn't want to go in, or at least we don't hear anything about it.

On the other hand, there are those who say he must have already been inside the law as he has been taken on into its service and that could only have been done inside. That can be countered by supposing he could have been given the job of doorkeeper by somebody calling out from inside, and that he can't have gone very far inside as he couldn't bear the sight of the third doorkeeper. Nor, through all those years, does the story say the