Edmund's character is probably the most ambiguous in the novel. For the first half of the book, Edmund is as spiteful and mean as it is possible for a young boy to be, but his character transforms halfway through the novel. By the end, Edmund is fair-minded and brave, and he is just as admirable as Peter. This is the whole purpose of Edmund in the novel. The Witch is simply evil through and through. The Witch has no capacity for goodness, possibly because she is not human and was therefore not born with the capacity for both good and evil that human beings possess. Edmund is human, however, and no matter how evil he acts while in the service of the Witch, he is never so far gone that he cannot redeem himself.
The Witch's enchanted box of Turkish Delight initially seduces Edmund. The magical candy causes an insatiable greed for more in the unfortunate eater. Edmund fixates on the candy to an excessive degree, even for a child. Edmund does not seem to care when he hands over his brother and sisters to a woman whom he knows deep down is a dangerous witch. Edmund sees more and more evidence of the Witch's cruelty and evil on, but he rationalizes her behavior. Originally Edmund is a traitor because of his greed for Turkish Delight. Later, it is evident that Edmund is corrupted by a desire for power and by the lavish promises of the Witch.
Edmund does atone for his sins and transform his character. The first change happens when the Witch treats Edmund like a slave rather than a prince. Edmund expresses his empathy and latent kindness when he witnesses the Witch petrifying a happy group of small forest animals. Eventually, Edmund fully realizes the Witch's intentions and the benevolence of Aslan. A discussion with Aslan seems to cement this change. Yet, it is not until Edmund stands up for himself in battle and helps slay the White Witch that he shows his true mettle. Most of Edmund's conversion occurred because of external factors—the Witch's cruel behavior and petrification of the animals at feast or the conversation with Aslan. Ultimately, it is up to Edmund to redeem himself and complete his transformation. This change takes a tremendous force of will and courage, but in the end, Edmund finds freedom. Lewis's message in a similar situation in another book is that "One wrench and the tooth will be out." It just takes one monumental effort and then we will be free.