One of the themes is that the author want his readers to know that there is more to life then we can see, or that a building/ strengthening a friendship is worth more than any treasure. Another one is like don't judge a book by its cover in this case the author is trying to point out when gandalf said that biblo is more than what meets the eye and thorin and co. underestimated him. Until he found the ring. Sorry if this is spoiling the book to anyone. Hope this helps! Have a great day!