Matty changes when he realizes he has a special power in the ability to heal.

This is the third book in the four book series following The Giver.

Matty has always known that he is good at being a messenger, because he can travel through the Forest unharmed by the warnings that others sometimes get, meaning the Forest will not let them come through again.  Since Matty is able to travel through the forest, the Village’s Leader sends him to a nearby village to get Kira, who can see into the future.  The Forest tries to attack him, and he ultimately is able to get Kira but is in danger.

Matty first discovers his talent to heal when he tries to remove a frogs injured leg and something weird happens.

But he felt a sudden jolt of painful energy enter his arm, concentrated in his fingertips.  Matty was unable to move. …. His pulse thrummed and he could hear the sound of it. (p. 44)

Matty is later able to cultivate and use his ability to heal things for more than frogs.  He uses it to heal the Forest, to bring it back to its more natural state and bring harmony to the Village.