Why does o'brien include norman's letter in the story?

The prefix of the italicized word in the sentence is rather difficult

Which best explains this excerpt’s purpose in the novel’s plot structure? the excerpt creates conflict between characters as part of the rising action. the excerpt provides background information on a character as part of the exposition. the excerpt returns a character to equilibrium as part of the falling action. the excerpt is the point of greatest tension and acts as the climax.

When mrs. jameson says "it (the desert) won't leave you cold," what does she mean?