Frankenstein has a complex narrative structure, and one of the things that makes the book difficult for modern readers is Shelley’s reliance on exposition to set up key plot points. For example, the opening chapters of the novel provide needed exposition about Frankenstein (though the device of Walton’s letters)—as discussed in this eNotes page.
Another example comes in Chapter 10, in which Frankenstein confronts the monster in the Alps, only to have the monster argue that Frankenstein “hear his story” before passing judgement. The monster’s “story” is a recounting of his life up to that point (six chapters’ worth!), including his learning to to love the De Lacey family by secretly observing them in their hut. The point of the exposition is to allow the reader to empathize with the monster’s acute loneliness, and sets up his demand in Chapter 17 that Frankenstein create a mate for him.
Extended expository passages like this one also serve to connect Frankenstein with the tradition of the philosophical novel genre. The back-and-forth between monster and Frankenstein here is akin to a philosophical dialog; Frankenstein’s final agreement to make a mate for the monster is a testament to the effectiveness of the monster’s story.