What are the religious symbols in "Sonny's Blues" by James Baldwin, and what do they represent?

In James Baldwin's "Sonny's Blues," there is a revival taking place as the narrator looks out his living room window of his house.  This scene is pivotal to the plot. For, when the woman with the tambourine is

divided by very little from the woman who stood watching her, a cigarette between her heavy, chapped lips, ...her face scarred and swollen from many beatings, and her black eyes glittering like coal.  Perhaps they both knew this, which was why, when, as rarely, they addressed each other, they addressed each other as Sister.

This religious encounter presages the redemptive realization of the narrator that he and Sonny are brothers; he senses that he must accept Sonny's invitation to come hear him play that evening. Furthering the understanding between the brothers is Sonny's telling the narrator that the singer's voice reminded him of what heroin feels like,

It makes you feel sort of warm and cool...And distant  And--sure.

As the brothers talk, Sonny explains that the heroin "makes something real..." out of the suffering.  The narrator tells Sonny, "But there's no way not to suffer."  Sonny agrees, but wishes that people would listen.

On the night that Sonny plays, the narrator truly does listen:

Freedom lurked around us and I understood, at last, that he could help us to be free if we would listen, that he would never be free until we did.

It is then that the narrator sees the drink for Sonny as "the very cup of trembling" that Isaiah tells of in the Bible.  This cup, much like the cup that Jesus in the Garden of Gethsemane asks to have passed from him, represents suffering.  At that moment, Sonny's suffering is lifted from him in his music and with those who listen.  Sonny's blues can help him to be true to what he is.