Explain why Hemingway begins the novel with this chapter

The narrator, Jake Barnes, describes Robert Cohn, who was the middleweight boxing champion of Princeton. Cohn took up boxing, though he disliked it, to compensate for the inferiority complex he developed as a Jew at Princeton. Cohn's nose was flattened while boxing, and Jake says no one he knows from Cohn's class remembers Cohn. From one of New York's richest, most prominent Jewish families, Cohn emerged from Princeton with low self-esteem, had an unsuccessful marriage, and lost most of his inheritance. Cohn's time in Princeton is almost an allegory of a young soldier's going off to war: his early dreams of glory are quickly shattered, his body is physically changed (the flattened nose), and he leaves embittered. He is quickly exploited by two women, the first instance of the theme of manipulative sexuality that Hemingway will explore in greater depth.