The fact that Peck mixes nonfiction and fiction in his semiautobiographical story confines this story to a particular setting. It must take place in a rural area, and the 1920s is the time period when a revival of interest in folk cultures led to the rediscovery of the Shaker religion in America. The setting is necessary in order for the story to be told and to maintain the authenticity of the autobiographical events.
Those who practiced the Shaker religion separated themselves from society, so Rob's feelings of isolation and mistreatment by others is certainly realistic. Some of the Shakers' most important beliefs were in hard work, the ownership of land, and the perpetuation of the community of Shakers. Their morality is shown by such proverbs as, "Never miss a chance to keep your mouth shut."
The farm setting allows the events dealing with nature and the animals to take place, such as the details of the cow giving birth. The characters are molded by their setting, and the closeness of the family is important. Even though they are poor, Rob's dad feels he's a rich man. His mother is characterized when Rob says, "I could smell her goodness". Rob's growth and maturity is seen as a natural result of the events of his life, and the reader isn't surprised when he accepts his role as the man of the house after his father dies.
Setting isn't always the most important element, but in this case, it truly is.