I think central to this excellent fantasy novel is the gradual transformation and process of maturity of Ged, who starts off in the novel as a wizard with tremendous ability, to being a mature adult who is able to control and use his power wisely. In many ways, this novel is a coming-of-age story, where we follow Ged's progress from being a rather arrogant and vain individual who is eager to show off his power for the wrong reasons, to the mature archmage that he becomes when he is able to face and confront his own mistakes and take ownership of them.
We see this most clearly in the way that he unleashes the devastating shadow upon Earthsea over a silly argument with Jasper about who is the most powerful magician. Personal pride and arrogance results in Ged setting a force of evil free that will torment both himself and others. However, at the same time, by the end of the novel, we see that Ged has matured so much that he is able to choose the good of others over his own personal benefit, such as when he does not make a deal with the dragon to gain the name of the shadow. At the end, when he confronts the shadow, he confronts the evil within himself. His recognition of this completes his coming of age and shows the final step of his maturity.