I suppose that I shall never be one who wants a book to read. Or, that is to say, wants for or lacks a book. I've got thousands of to-be-read books sitting in piles in my old bedroom, back at my parents' house, and more scattered about here. It's quite unseemly.
But that likely isn't Chesterton's point, anyway. An eager man who wants to read a book might pick up anything, just to show that he's reading. Or he might be eager because he already knows the book he wants, and has high expectations for it.
The tired man who wants a book to read may want it for comfort, or to relax after a hard day. He would probably want something familiar instead of challenging, but that doesn't mean he wouldn't still get something out of it.
Hmmm. The more I think about this quote, the less certain I am of the point Chesterton was getting at. And I'm sure it's perfectly obvious, too. How embarrassing.