What are major themes?

In literature, a theme is the overall lesson that the writer wants the reader to learn from the book based on the actions and the events of the story. A single work of literature can have many themes, but it is usually based on the individual reader. Clues to discovering the theme of a work can be seen in what the characters learn in the story; for example, one of the themes of Harper Lee's novel To Kill a Mockingbird is to not judge a person based on their outward appearance but rather their inward character. We can see this by how Scout, the protagonist, treats and interacts with Boo Radley, Walter Cunningham, Jr., Tom Robinson, and Bob Ewell, to name a few. We can also determine theme based on recurring ideas that a present in the story. For example, Atticus Finch teaches the lesson of treating others equally in To Kill a Mockingbird when he takes the case of a black man in 1930's America when tension between races was high. We can also see that theme of treating others as equals is present by how he treats Walter Cunningham, Sr. and Bob Ewell and by how he teaches and corrects his children.

In literary terms, major themes are—as they sound—the most prominent and usually the most important themes that are present throughout a novel. Typically, these themes are consistently present for the duration of the novel and are obviously presented. They are not subtle or difficult to detect. For instance, some of the major themes of To Kill A Mockingbird include racism, prejudice, and loss of innocence. These themes are present throughout the novel and consistently tie into the plot and story line.
Major themes of a novel are often the most important concepts that an author wants readers to focus on and ponder. Major themes can also be reflected in the genre of literature. For instance, a major theme of a romance novel is love. A major theme of a book on the civil war is, of course, war. However, major themes can still be incredibly specific to a novel through the manner in which they are represented and through the story that is told.