It can be hard to pinpoint an exact definition of theme because there is not always a single right answer when describing the theme of a piece of literature. In general, the question of theme asks what a book means on a deeper level. Theme is the lesson that can be learned or a statement that is made from the events in a book or story.
A story's theme does not relate specifically to a character in the story, but speaks to any reader of the book who can understand the character's experience. Many themes provide commentary on sweeping topics like marriage, war, coming of age, time, death or God. Themes can be simple or complicated and are always prone to debate. For example, in a story about two people who fall in love, the theme may be the role of marriage in human fulfillment or about how individuals learn to relate to one another. In a story about a person who dies too soon, the theme may be the fleetingness of life, the necessity of death or even a commentary on healthcare or standards of living. Theme can be interpreted differently by different people, and it's common for stories to have multiple themes.
The theme of a book won't be directly stated in the last chapter. Instead, theme is something you have to analyze on your own. To brainstorm the themes of a piece of literature, try to summarize the entire story in one word. Consider the lesson a main character has learned at the end of the story. You can even ask yourself what you learned from the story. If a definitive moral statement or idea comes to mind, that's probably a theme of the story.
Theme helps us to identify the author's purpose in writing a book; more often than not, it's more than just to tell a story. A story will become more worthwhile when you dig past its surface to find out what it really means. Theme can also help you understand the cultural and historical context of a book; that is, the conditions of the people who lived at the time and place the book was published, and what the book may have meant to them. The theme of a book is the greater message you take from reading it and the reason you come back to it over and over again.