The fact that the family lives in a very precarious place - next to a mountain where there have been many landslides and that a slide can occur at any moment -- is significant in this story because at the end, a slide does occur and the family and the guest are killed. Nature represents fate in the story, I believe. Neither the family nor the guest has any control over what happens to them in the story, in spite of the "ambitious" plans of the guest. The fact that the family members have not achieved any great accomplishments and the fact that the guest, despite his plans, has not achieved anything all become irrelevant when they are all killed - by an "act of God" out of their control (nature). The irony of the story is that in spite of his plans, no one remembers the guest, but they do remember the family members by the little tokens they left behind. So nature is used in a symbolic sense to illustrate forces beyond our control in life.
Read about the story here on eNotes.