What does my teacher mean when she says this?

I have to write a report based on a novel I read. While the novel plays a big part of the report.. I don't understand what I am supposed to do. She says I have to discuss central aspects of novels that includes themes, symbols, motifs, style, characters, author's bio, structure, events surrounding the publication. Shee says to define the author's purpose and how devices contribute to the communication of the purpose. I'm confused by the 'author's purpose'? What does that mean? Themes? Can someone please help me? Thanks.