What is the purpose of the "frame narrator" at the novel's opening and close?

The frame narrator serves a few different purposes in the novella. First of all, it allows the novella a personal perspective. By telling the story from a first-person witness account, there is more credibility and realism associated. The frame narrator also allows for commentary about actions and motivates that might not be seen otherwise. The narrator is able to give his own interpretation of people and events without being personally invested in the story. It also adds an element of suspense to the story. The audience doesn't receive information omnisciently, they receive it as the narrator relays it. Finally, and perhaps most practically, this form of narration was very popular at the time. Frankenstein and The Scarlet Letter both employ similar uses of frame narration, and both are also considered Romantic literature.