What is significant about the introduction of Robert Cohn before the narrator, Jake Barnes,

Hemingway deploys his influential style of spare, unadorned prose to good effect here; in giving a run-down of Cohn's character, Jake reveals himself as a quasi-reporter (indeed, he works for the newspaper, though not as a reporter, and Hemingway himself was a former journalist) who does not reveal much about himself. Jake doesn't even tell the reader his name -- we only find out when another character calls him by his first name -- or about his job, but lets you in on both his factual and emotional life through others.