The poem is an amazing statement about life in the South and the disconnect between the promises and possibilities of life in America and the reality that confronts people of color.  I would strongly suggest listening to the Billie Holiday rendition of the poem in song form to help bring out the torment and mournful tone of the work.  The second stanza is significant in this light.  The opening lines of the stanza help to bring out the unbridled hope and glory that is a part of the American social dynamic.  The scope of the "pastoral sight" is expansive and the "gallant" descriptor of the South is a realm in which there is a sense of the regal and glorious evident.  These notions are offset by the vision of those who are lynched, hanging from trees with "bulging eyes and the twisted mouth."  These visceral images of the bodies being hung for simply being Black is meant to be a contrast, a pivot to what is as opposed to what is being depicted.  The third and fourth lines follow the same pattern with the magnolia flower being "sweet and fresh" being contrasted with the literal and figurative burning of flesh and the smells associated with that.  These contrasting images help to bring out the gulf between the promises and possibilities of the American landscape regarding race and the images of what America is seen as.  The contrasting images help to bring out this gulf of both perception and reality when it comes to America and racial identity.