The "Key" Note.

"Let's us strike the key-note again, before pursuing the tune." The title of Chapter 5 is titled "The Key Note." I was rather curious upon what this meant in the context of the current chapter and its effect on the upcoming chapters. So, I did some research and found out that according to the dictionary, a key note (in literature) is a main idea/principle that establishes underlying theme. With your individual knowledge and understanding of the pages and chapters that you have currently completed/read, what do you believe is the underlying theme that has been the basis of this story so far? What have the characters experienced through out these Hard Times? What is the "key-note" that keeps striking the story, providing the readers with a certain type of tune of mood?