The tree is used as a training site for seniors enlisted in the military to simulate the abandonment of a torpedoed ship. An excited Finny urges all of the boys to jump off of the tree into the Devon River with him, for he thinks that the war is a fun game just like any sport.
Gene remains terrified, however.
Finny sleeps without wearing any pajamas because he is trying to be like a soldier even though he's still a schoolboy. Gene and his fellow schoolboys are somewhat admired by their teachers for their playful innocence. For all of the boys, Finny embodies the spirit of this innocence as well as the peace that occurs because of it. Devon makes him feel safe and at peace. War seems like just another game for him because of his innocence and inability to understand how to hate or want to kill.