It is Shreve who asks Quentin to tell him about the South. Had a person from some part of the United States requested the same from Quentin, it is highly probable that he would have told a completely different story. But the important thing is that Shreve is not a United States citizen. As a Canadian, Shreve is familiar with the history and events which have molded the American culture, but his knowledge has come from history books, not from being involved in living that history. Quentin must have a listener who is objective and yet responsive. Shreve has those qualities necessary for a good listener. He is sympathetic, he has a sincere desire to learn more about the South, and he is not prejudiced with preconceived ideas which would prevent him from responding objectively.
With these qualifications, we see the value of Shreve as a listener. A person from any part of the United States would have constantly had objections to Quentin's story. On the contrary, Shreve is able to respond to the story in a detached manner. There are no regional prejudices or sectional loyalties involved in his response. Thus by choosing a person outside the United States, Faulkner is able to obviate the regional preconception and prejudices of the reader, and it becomes more the reader than Shreve who is the fourth person on the ride back to Sutpen's Hundred. By choosing the most objective person as the listener, Faulkner is able to subjectively involve the reader in his story, thus universalizing the narration.