The function of a prologue in literature is multi-dimensional. A prologue is a short introductory piece included at the beginning of a novel, play or poem. It can be as short as a poem with a few lines or as long as a full-length chapter. It can serve several purposes, including giving background information, establishing the tone and setting, hooking the reader into the story, and introducing characters and conflicts.
A prologue provides background information for the reader. It can introduce incidents in the past that are important to the current story. Historical happenings that are critical to the plot and characters in the story can be highlighted, although they also may be given more description later. Fiction works that have prologues sometimes would not be as easy to understand if they did not include a prologue to provide background information and introductory exposition.
Another function of a prologue is to establish the tone and setting of the story. If a novel is to have a mostly somber and serious tone throughout, then this can be established in the prologue so readers have an idea of what the whole story will be like. The setting also can be introduced, because where and when a story takes place also can be essential to how the plot and conflicts play out and are resolved or extended.
For novels and plays, another function of a prologue is to hook readers into the story. The small part they read in the prologue may have just enough information or interesting situations that they will want to read further. Especially when prologues are short and provide only cursory information, they serve to heighten the interest of readers quickly so they will want to continue reading. Prologues are sometimes read in much the same way as a book jacket — before readers actually decide whether they want to read an entire story — so a fascinating prologue can hook them and make them want to keep reading.
Prologues also exist to introduce characters and conflicts, especially when they are presented as preliminary chapters. They can go ahead and let the reader see inside the actual story and learn what has happened and what may happen in the future by letting them in on the action and the characters. Besides just hooking readers, prologues that are full chapters or episodes in novels or plays can set up the fascinating personalities of characters and their interactions, relationships and conflicts with one another and with the world at large.