The quote first appeared in the book. Krakaeur attributes the quote to Ronald Franz, an older retired army man. Chris met Franz (this is a pseudonym for the actual person) is Salton City, CA in 1992. Franz had lost his family in an accident long ago and was a recovering alcoholic. He and Chris formed a father-son type bond.
According to Krakaeur, Franz was a devout Christian who would question Chris' lifestyle and choices often. It seems that Krakaeur's intention in describing this relationship is to show how determined Chris is to continue on his trek "Into the Wild" and away from all human civilization. Despite the bond Chris forms with Franz, he still chooses to move on, declining Franz's offer to adopt him as a grandson.
Sadly, Krakaeur reports that Franz returned to drinking upon hearing about Chris' death.