Chapter IV is a key chapter both dramatically and thematically. In terms of the novel's action, it is when the protagonist of A Farewell to Arms meets the novel's heroine, setting the story proper in motion. Notice how quickly they become intimate; Catherine Barkley talks of her recent loss of the man to whom she was engaged, and the narrator admits that he has never loved anyone. Hemingway understands how rapidly people grow close during times of extraordinary stress.
Thematically, the narrator is already preparing for — that is, rationalizing — what will be the climactic act of the novel: his desertion from the Italian army. He does so here by telling himself and us that his leave has not affected the smooth and successful operation of his unit: "It evidently made no difference whether I was there to look after things or not" and "The whole thing seemed to run better while I was away." In other words, if the narrator chooses to abandon his commitment to the cause someday, this will have no discernible negative effect on the war. Along these lines, Miss Barkley's observation, "What an odd thing — to be in the Italian army," is significant, the first of many such remarks that will give the narrator a kind of permission, ultimately, to desert. After all, he joined voluntarily, and it is not even his own country he is fighting for.
