This chapter establishes Valentine's importance by showing that she is the only person in the story who truly cares about Ender and the only one whom he will miss. Peter, on the other hand, seems to need no one, and so it is important that Ender places his faith and trust in at least one other human being. Without his feelings for Valentine, it is not clear that Ender could maintain that empathy that separates him from his brother. It is not a coincidence that the last voice Ender hears as he leaves home is his sister's—hers is the voice that he needs to take with him wherever he goes. The I.F. believes he needs some of each of his siblings to save the world, but Ender does not want to be Peter at all.
Ender's parents have very little role in Ender's life, and it is clear that their children are more intelligent and more interesting than them. However, what Graff tells Ender about his parents' past is significant. He points out that Ender does not really belong at home. As a Third, Ender is a constant psychological torment to his parents. Ender knows that he makes his parents uncomfortable, and hearing Graff spell it all out makes it easy for him to leave. The only thing that is difficult for Ender is walking away from his sister. He leaves behind the one thing he truly loves in life for humanity's sake. Ender is sacrificing what matters to him because he wants to do what is right. Levels of manipulation are often subtle in this novel, and Graff is able to convince Ender to come without lying to him—he just does not tell Ender the entire truth.