Mary Shelley's novel Frankenstein opens with four letters Robert Walton writes to his sister Margaret Saville. The reasoning behind the letters is three-fold: to let his sister know of his safety, his intent, and of the story he comes to hear from Victor.
The opening letter defines Walton's intent to insure Margaret of his safety.
You will rejoice to hear that no disaster has accompanied the commencement of an enterprise which you have regarded with such evil forebodings. I arrived here yesterday; and my first task is to assure my dear sister of my welfare, and increasing confidence in the success of my undertaking.
With this opening, readers are made very aware of Walton's connection to his sister. readers are also made aware of the fact that Margaret worried about Walton's expedition.
Secondly, Walton writes about his intent to traverse to the North Pole in order to prove "the inestimable benefit which [he] shall confer on all mankind, to the last generation, by discovering a passage near the pole to those countries." His passion since childhood, Walton is living his ultimate dream.
Lastly, upon the arrival of Victor to his ship, Walton is left with a story which proves to be utterly horrific. In the final letter to Margaret, Walton sates the following: "You have read this strange and terrific story, Margaret; and do you not feel your blood congeal with horror like that which even now curdles mine?" (Chapter 24)
While some readers may have forgotten that Walton serves as the true narrator of the entire novel, given his desire to continue his letters to his sister as part of his attempt "to record, as nearly as possible in his [Victor's] own words," Walton's letters truly serve as his recording of Victor's tragic story.
to record, as nearly as possible in his [Victor's] own words, what he has related during the day. If I should be engaged, I will at least make notes. This manuscript will doubtless afford you the greatest pleasure,....