Answer:
The theme of the story was developed by the two main characters, and how they interacted and thought. They had been cellmates at one point, but now they both were in a prison camp, and one was living in moderate comfort, while the other was laboring in the mines. The difference in their material possessions and positions in the prison camp is shown by how they act, and what they wear, and their desires. The cellmate who worked in the office wore good shoes and checkered socks, which are pointed out because the other man only had rags to cover his feet, and how the miner wanted what the office man had, but he knew the difference in their statuses. When the office man offered the miner man a way to escape, he knew that it couldn't be true and that the office man was selling out fellow prisoners for money, because why would the office man want to escape? He had possessions and lived in mild comfort, he had all he needed, but he knew his fellow prisoners longed for material possessions and wanted freedom. That is how the theme was developed, by the longing for condensed milk, a delicacy to the miners, but a normal product for the office workers. The condensed milk would only satisfy for a little while, but it was satisfaction and enough for today.