It's not even a light novel it's just a normal novel. I watched the anime twice and read the novel once. The novel was the last time I revisited the series but I might again soon. It is definitely an all time favorite of mine.
The "message" is kind of irrelevant and the author himself didn't live up to it. He lives as a hikikomori on the royalties of the book. I don't know what he's doing now. The true moral of the story is write a book about rotting and continue to be a rotting hikikomori on the profits.