Like millions of others around the world, I bought a copy of the final Harry Potter book last Saturday and promptly read it. Twelve hours later, I was finished, astonished, at the brilliance of J.K. Rowling. She has woven a universe of magic, not just in her writings, but in the fact that more than a hundred million children over the years have turned off their televisions, computers, and games and sat down to read thick books. What explains the attraction of her work? Sheer brilliance. The clarity of her vision remained unbroken despite the complexity of her creation. Readers...