How does Chris Crutcher use imagery in The Sledding Hill?

Imagery:

“If humans are ever to understand one another, they will have to come to terms with the concept, and the reality, of relativity. In essence, that’s what the Earthgame is about. They will have to see how things look compared to other things. Once you understand that nothing exists without its opposite, you understand nothing is good and nothing is evil, that opposites actually hold each other up.”