How would story change if it were told by Sonny?
Music promises freedom to Sonny from the blues of his life. He has used heroin to give him a short respite from his sufferings, but Sonny realizes heroin will eventually kill him. So if Sonny were telling the story, he would tell it with his music because this is the only way for him to express his feelings in a positive manner. Thus, the short story would be told through jazz, so we would realize just as Sonny's brother did that "he could help us to be free if we would just listen, that he would never be free until we did."