Chapters 27-30: The Ghost of Tom Joad

Tom does something very selfless in order for the family to not have to live with the fear of him being caught and them being accused for hiding a criminal. Essentially, everything that is wrong with the country as this point in time sort of represents Tom. Police beating folks for trying to survive, the rich farmers hardly giving workers a dime, etc. Tom is that. He is the struggle that is going on throughout all of these family's lives. I am unsure if Steinbeck intended for that connection to be made when writing this, but it is something that finally clicked in my mind as I was nearing the end. 
After Casy dies, Tom changes his view on life and in a way, becomes the new Casy. It's not that he obtains an abundance of knowledge on life, he just starts to see things differently. In his last conversation with Ma, he tells her that even though he will be gone, he will still live on in everything that the family endures and must go through during their struggle to restart their lives. 
When you think of ghosts, you picture mysterious sounds or shadows dancing across the floor. Ghosts are not visible, and to the rich farmers, migrants are invisible as well, as if they are ghosts. 'The Ghost of Tom Joad' is not just about Tom becoming a ghost when he disappears, it is about all of the Okies that have moved West in search of work but found themselves become transparent when it came to obtaining work and being able to live like humans should, rather than sleep in dusty tent camps along the sides of roads. When you have everything that you want in life, you tend to not see the needs of others, and only care about your own problems, not matter how more fortunate you may be than them. The idea of this rich vs poor society is merely ghosts and the people who fear them.