The introduction to The Prince and the Pauper works as a frame story, putting the main action in the context of the narrator’s life. In the introduction (“The Great Seal”), Twain's narrator says he is going to tell a story that someone else told to him—and that person heard it from his father, who heard it from his father before him. In fact, the narrator claims the story can be traced back 300 years or more, "fathers transmitting it to the sons and so preserving it."
The frame story sets the novel up as a folk tale which has been passed down from an unnamed source, and from his father, and so forth. It is interesting to note that the story has been preserved from father to son, given the importance of father-son relationships throughout the story (between Tom and John, Tom and father figure Father Andrew, Henry and Edward, etc.).
The narrator uses the frame story to establish the value of the novel. Fathers have consistently “ transmitt[ed] it to [their] sons,” believing that their sons have something to gain from learning it, a narrative which sits well with the didactic elements of The Prince and the Pauper. Thus the reader, presumably a child, is put on notice, and feels he must pay careful attention to the book in order to see what is so important about it.
The narrator also admits that the novel “may be history,” but equally “may only be a legend.” The novel, though a children’s story, is based on real historical events and figures fancifully reimagined by Twain. Perhaps anticipating disbelief from the reader (particularly from any children who have done their research on the Tudors), Twain’s narrator describes the story as one that “could have happened.”
The narrator implies that while the story may seem incredible, its veracity is actually unimportant. Regardless of its historical truth, he says, the story has endured because it has something to offer everyone (“It may be that the wise [...] believed it [...] it may be that only the unlearned [...] loved and credited it”). Through this imagined provenance of the novel, Twain suggests that, accurate or not, the novel that follows holds something valuable for all readers.