What is the thematic purpose of Chapters 4-5 from Into the Wild?
Chapters 4-5 deal with Chris's movement from a driver -- almost a tourist -- to a legitimate vagabond, a title in which he delighted. Chapter 4 shows how his car was disabled by a flood, and he used that as an opportunity to divest himself of overt connections to his prior life. Chris believed that material possessions weighed him down spiritually, and so he was happy that he had the chance to create a physically and emotionally lighter persona. It also shows the joy he took in wandering without a specific purpose, preferring to be free of obligations and responsibilities.
Chapter 5 shows the personal connections he made in Bullhead City, and how despite his aversion to civilization he felt the need to live and work for a time, perhaps to recharge some mental batteries for his future isolation. Jan Burres, a friend with whom Chris corresponded, mentions her own theory:
"He needed his solitude at times, but he wasn't a hermit. He did a lot of socializing. Sometimes I think it was like he was storing up company for the times when he knew nobody would be around."
(Krakauer, Into the Wild, Amazon.com)
The interviews in this chapter show Chris's refusal to conform entirely to social norms, and the deliberate way he remained aloof from real emotional connections. The chapters taken together show how Chris codified parts of his personal philosophy, and how he prevented himself from falling back into the comfort and ease of civilization.