A theme is the general message or statement about a subject that all the elements of a story or a poem work together to develop. Without a unifying theme, a story contains only arbitrary events and characters. Theme functions as the understated but essential ingredient to make a story or poem meaningful.
Every work of literature contains a stated or implied general message about life and the world. These truth statements about how the world works, or at least how the narrator has observed it to function, are usually debatable, but they're not necessarily revelations: If they were, they might not resonate with readers. For example, the theme of absolute power corrupting absolutely appears in a range of works from "Macbeth" to "Animal Farm," the difference existing in the settings and characters -- kings and barnyard animals, respectively. Stories that contain unbelievable or unrealistic statements about human nature -- say, that people aren't greedy for power -- are unconvincing. Without at least one seemingly truthful theme, a work of literature falls short.
A moral position lurks within every story, regardless of whether the narrative actually promotes a moral solution. The story may illustrate a problem with the world while going no further to offer a solution or suggesting what people should do about it. Questions about right and wrong and how our consciences move or fail to move us have a place in every story, whether direct or implied. "Jude the Obscure," by Thomas Hardy, depicts the devastating effects of a stifling marriage and implies that the cause of many failed marriages is the institution of marriage itself. The author's suggestion that marriage should be revamped is a controversial solution to an acknowledged problem. The problem is the theme; the solution is the moral message.
An author's choice of literary and stylistic elements -- such as plot, character, narrative style and symbolism -- affect the development of theme, and theme functions to unify them all into a coherent presentation. English professor Linda Lovell from Northwest Arkansas Community College describes theme as the "thesis" of a fictional work. As in a formal essay that makes an overall statement and then proceeds to prove its argument through examples, a theme in fiction functions similarly, only it uses character, plot and other literary elements to make its case.
Themes are important, but when you're reading a story or poem, you may not be cognizant of them and how they play on your emotions or influence your perspective of the subject matter. To identify the theme of the story or poem you are reading, consider what insights the theme offers about the world that could apply universally to anyone or any situation outside of the text. If you are writing your own story, develop your theme by organizing the events in the plot, the flow of narration or the feelings and thoughts of the character around a subtle moral issue. Literary works can contain multiple themes; usually, however, one functions more prominently and they all need to work together in a believable way to incite appreciation or sympathy in a reader.