Which single sentence in chapter four best states Casy’s new thinking about the nature of sin?
The original question had to be edited down. Casy's explanation as to why he has found a new path that exists outside of the institutional construction of the church can be found in his new form of thinking. When Casy speaks of his new understanding, I think that it becomes the lucid expression about his new thinking about the nature of sin: "There ain’t no sin and there ain’t no virtues- There's just stuff people do.” This becomes critical in how Casy sees the nature of sin. For Casy, the distinctions of "sin" and "salvation" are hollow words when divorced from action.
Casy has moved into a realm where actions are what supports the nature of sin and the nature of how people behave. His movement away from the traditional structure of the church is rooted in his belief that the actions people take, what they do in facing the need to help others, is where salvation lies. Casy is at a point where he can see people as more than "good" or "bad." Rather, they are complex. Casy himself realizes this, recognizing his own motivations are intricate. In freeing himself from the reductive understanding about human action, Casy has been able to construct a new form of thought about the nature of sin and human beings' role within it.