There are several themes running through this famous work. For a detailed discussion of them, you might visit the section of the enotes study guide you can access via the link included below. In brief, though, the book is about where identity comes from. Do people choose who they are and what they do, or is it innate? Or is it due to their upbringing? This means that responsibility is a related theme. Working in opposition to this is the idea of fate—that things have to work out as they do. A desire for justice, which may be a desire for revenge, is a third theme that links both of these. Who will be punished, and what is the right punishment?