With suffering as the main theme of James Baldwin's story, one way to examine this theme is through the development of Sonny's character along with the narrator's that are often "trapped in the darkness which roared outside." For both men there are moments in which they have the blues and suffer in the darkness of their lives, but music takes this suffering from them.
Music also helps the narrator to understand his brother's suffering as, sitting in he darkness at the night club, the brother finally really hears the music in the manner in which Sonny has heard the street singer. In the night club, the narrator hears evocations that pull the storm from his and Sonny's souls. As this "triumph" occurs, the narrator sees the scotch and milk that the waitress brings to Sonny as "the very cup of trembling"--the symbol of the suffering and trouble sonny has experienced--and the narrator understands there in "the indigo light."