What is the main conflict in Messenger by Lois Lowry?

Young Matty is struggling to understand his strange and mysterious gift of healing powers just as the altruistic society he lives in begins to experience disharmony. A growing group of citizens demands to close its borders. At the same time, the Forest that once welcomed Matty now darkens and thickens to prevent passage. When Matty's caregiver, Seer, enlists Matty's help to travel through the Forest and return with Seer's daughter before the border closure, Matty must call upon all of his courage to journey through increasingly dangerous Forest.