I just ask myself.
Why am I going to read this book? It's amazingly powerful in it's simplicity. Some will answer things like "to learn". I'm sorry that's lazy. If your answer is something like " I'm looking for the answer to X, and I really need to solve X". That's the kind of purpose that will charge you. Unfortunately we don't always have so strong a purpose. Work with what ya got.
What do I want or hope to learn from it? This is another simple question I use to define a purpose.
