I am putting down this promise in black and white so I don’t ever forget it. When I grow up and have a kid I will never make him do anything he really does not want to.
-- Peter (chapter 6)

Importance: Peter agrees with his Grandfather in that there should have been a family conference instead of just telling Peter that he had to give up his room. Peter vows that when he is older and has children that he won't do the same thing to his children because he knows what it feels like to have it done to him.

Listen, Pete,’ Grandpa said slowly. ‘The only time you have to fight a war is when someone attacks you. Then, and only then, you have a right to defend yourself…War is no game, Petey…only kids and fools and generals think that…War hurts…war wounds and kills and causes misery...
-- Grandpa (chapter 22)