What quote in the book emphasizes the theme of good vs. evil?

This is the same quote I gave you earlier. It is the perfect quote to emphasize the point you're attempting to make.

"I believe that there is one story in the world, and only one. . . . Humans are caught—in their lives, in their thoughts, in their hungers and ambitions, in their avarice and cruelty, and in their kindness and generosity too—in a net of good and evil. . . . There is no other story. A man, after he has brushed off the dust and chips of his life, will have left only the hard, clean questions: Was it good or was it evil? Have I done well—or ill?"

Source(s): East of Eden

Here are a few others;

"Monsters are variations from the accepted normal to a greater or a less degree. As a child may be born without an arm, so one may be born without kindness or the potential of conscience." (Chapter 8)

Maybe we all have in us a secret pond where evil and ugly things germinate and grow strong. But this culture is fenced, and the swimming brood climbs up only to fall back. Might it not be that in the dark pools of some men the evil grows strong enough to wriggle over the fence and swim free? (Chapter 13)