Hesse slides in somethings with such subtlety that you can easily miss them, and you don’t want to blame him for that (Ha!). For you believe in the truest of your heart that he meant no guile in you missing that point – this isn’t a master story teller running a suspense job, but a fair person having a fair conversation.
The said element of interest here is metafiction. In the extended stage setting preface, the narrator describes Haller and then laments that he got too carried away in the description, and ended up disclosing more than he wanted to the reader, thus, subtly confessing to the reader that there is a reader and there is a writer, and such is the frankness and the directness of the communication between them that the writer is not willing to go back and tear away a page which he has written contrary to his plan. To quote Haller’s words from a bit later, “Is that not witty?”.
This reminds me of frequently written “PS” note in an email. Of course it was very meaningful in the olden paper times – if you thought of something after writing (post script) the main portion, it was easier to address the additional thought as a post script rather than rewriting. In electronic times, its utility is more doubtful, so it is almost never seen in electronic documents, but occasionally makes its appearance in emails. Now, if the sender thought of something before sending it, why don’t they go ahead and change the content anyway, rather than using a PS construct? Or perhaps the sender means it as “Post Sending”? 🙂 The answer clearly lies in a metafictional sense as well – the sender of the email would really like to convey that this additional point is merely a PS, perhaps in an attempt to deemphasize it, even if it is the most important point the writer makes.