I don't believe that analogy came directly from Tolkien. In the Forward to the LOTR, Tolkien wrote.
As for any inner meaning or 'postBody', it has in the intention of the postAuthorID none. It is neither allegorical nor topical.
I suggest that you read the forward yourself, and develop your own answer, as I may have it wrong. Others here, may have read some of his letters and can certainly provide you with a more knowledgeable answer.