Basically it describes a nightmarish situation which most people can somehow relate to, although strongly surreal. With an ethereal, “evil”, omnipotent power floating just beyond the senses.
You point out that you can easily go into the building, and the guard agrees. Rather than be disagreeable, however, you decide to wait until you have permission.
You wait for many years, and when you’re an old, shriveled wreck, you get yourself to ask:
“During all the years I’ve waited here, no-one else has tried to pass in to see the law, why is this?”,
and the guard answers:
“It is true that no-one else has passed here, that is because this door was always meant solely for you, but now, it is closed forever”.
He then procceeds to close the door and calmly walk away.
This is in fact, one of his short stories, and is very typical to his style, i.e. kafkaesque.