What is the difference between theme and subject?
The subject of a book, short story, or poem is what it is about, but the theme is the moral or lesson. For example, Great Expectations is about a young boy who is given a fortune from a secret benefactor so that he can become a benefactor. That is the plot. The theme is that you should care more about people and love than money. While focusing on money, the young protagonist Pip becomes an awful person. He realizes after some tumultuous events that people are more important than money.
Books have more than one theme usually, depending on their length and complexity. You can determine the theme by the message the author is trying to convey to the reader. The topic of the book, story, or poem will be related to the theme because authors use a story to convey the theme.