How does Bree help Shsta develop and grow

Shasta is young man who was kidnapped at birth and sold into Calormene slavery who over the course of the book plans to escape from his abusive master with the help of a talking horse named Bree. It is revealed that Shasta is actually Cor, the older twin of Prince Corin of Archenland. His kidnapping was to prevent him from fulfilling his destiny of saving Archenland from destruction.

Bree, a talking horse, is the companion of Shasta. Like Shasta, he was captured by the Calormenes as a foal. He and Shasta plot to escape from their slave masters, leading them eventually to Archenland where they discover Shasta's true origins.