Borges packs a wide range of ideas into this short story, and his tone shifts depending on what he's talking about. When he presents us with the concept of the Library, he's objective and matter-of-fact in his description. When he raises philosophical questions, he's serious. When he describes the follies of the Library's inhabitants (suspiciously similar to some of our own) he's witty. He's both playful and imaginative in his invention of new symbols and allegories. And when he describes the narrator's pain at not succeeding in his life-long mission to understand how the universe works, Borges is sympathetic. Hey, he's a complexly emotional guy. And that's why we love him.