This is novel is rich in imagery, and sometimes personfication adds to the picture that is created for the reader. Personficaiton is the assigning of human qualites or abilities to non-human things, and this figurative language helps the reader better picture what is being described.
Here is an example from the opening frame chapter. When the narrator is telling what the Frome house looked like, he desrcibes the run-down and worn-out conditions, claiming that "the thin wooden walls . . . seemed to shiver in the wind." Obviously walls can't shiver, but the image of walls that are shivering or moving subtly with the wind enhance the fragile and broken condition of the house, especially in the snowy and windy weather.
Another example is when Ethan and Mattie are together in Chapter 4 and the narrator explains that they "had stood there with such a thirst for each other in their hearts." They aren't literally thirsty, and a heart can't be thirsty, but everyone understands what it feels like to be thirsty -- to want to beverage to sooth a dry throat or a parched mouth. It can be a singularly intense instinctual need, and that is what is being conveyed here about how they feel about each other.