Where does the power of transformation come – from the inside or the outside? In Bridge to Terabithia, it's both. Through their friendship, both Jess and Leslie are changed for the better. Jess becomes more imaginative, and Leslie becomes more compassionate. They each teach the other about becoming a better person. But becoming a better person also comes from within. In teaching Leslie compassion, Jess strengthens his own capability for it, and in leading Jess into Terabithia, Leslie expands the boundaries of that realm for herself. They learn to see other people as their friend sees them, and make a more ordinary kind of transformative magic for themselves by imagining Terabithia.
Without Leslie appearing in his life, Jess might have become the fastest runner in fifth grade, but he wouldn't have learned nearly as much about courage, imagination, and a potential larger world.
Through her encounters with Jess, Leslie also learns about the complexities of the world outside Terabithia and how, in order to be truly good, it's necessary to find compassion for even the scariest enemy.