What is the lesson learned in Bridge to Terabithia?

One of the main themes in the novel is friendship, namely the friendship between Jess and Leslie. The novel highlights the importance of friendship and how it helps a person develop at a personal level. Jess and Leslie grow and mature because of their friendship and they also learn how to deal with a reality that is often painful through their friendship. Jess and Leslie complete one another and they also push themselves to achieve their dreams and discover new things about themselves. What is important is that through this friendship Jess and Leslie are strengthen by their relationship and they both reach a level of maturity that would be otherwise hard to achieve.