Poverty and trains
Through a classical depiction of poverty the reader understands that William Music is a symbolic character who represents an entire category of people. He is a wanderer and a vagrant, unwanted by societies, though he would be a good employee to someone. His station makes him unappealing to the eye, and so he makes his way back to Virginia the only way he can, by risking dangerous and illegal passage by train. He is not a bad person, but a good person beset by bad fortune.
Kentucky coal mines
The coal mining town features work of one kind: coal mining jobs. These jobs are defined by blackening imagery. The coal is black, and the workers are covered in it. They go underground into the dark caves and mineshafts, which sometimes collapse, killing people or burying them underground beyond help. The risk is great, and the reward is meager. They work for a hard-faced employer who is unhappy with the economy and who wants to save something of a profit—even if he has to disenfranchise his own workers to get it.
The town ecosystem
Through abstract imagery, we learn that the town is an ecosystem that functions by delicate balance. The ecosystem can be easily tipped, and when the union comes, it comes with enough weight to permanently change the town, for better or for worse, probably both. The ecosystem is one that Music has to learn and endure as a newcomer. He realizes that these people are often orderly and straight-forward, but these days, the Depression has made for political instability.
Power and class warfare
By the end of the novel, the imagery is clear. The story is of lass warfare. The threat of poverty has made the working class less patient with the domineering boss, and the union has made the boss into a paranoid control-freak who defeats his own interests by becoming exactly the kind of boss that the workers must not tolerate. He introduces guns into the equation and starts drawing lines in the sand. Before long, it is a full-blown battle—a symbolic depiction of class struggle.
