Steppenwolf- Where does the preface fit in?

For me, one of the parts of Steppenwolf that got me thinking was the preface. It is a fictional intro to the main body of the book, which is purported to be a manuscript written by Harry Haller. The preface is by a fellow lodger. In it, he states that he doubts that the events in manuscript are real, and that if he had not met Haller he would have immediately dumped it in the trash. At the end, he says that he will leave it up to the reader to make up his mind for himself.

The manuscript contains a strange tale, and I am not sure how to interpret it. It is interesting, though, to put it in the context of the preface. The reader is reminded that Haller's story may be just words on paper. On the other hand, the author of the preface is an ideal example of just what Haller despises in the middle class. The author would throw the manuscript, which is about Haller railing against people like him throwing something like that in the trash, in the trash. In the end, though, he doesn't, because Haller made an impression on him. I hope that makes sense.

In any case, I certainly thought the preface added an extra level to what was a very good book. Anyone else have any thoughts?

I think the preface adds a lot to the story and makes a perfect introduction to the character as an outsider.