The clarity with which Rowling sees the need to choose between good and evil is admirable, but still more admirable, to my mind, is her refusal to allow a simple division of parties into the good and the evil. Harry Potter is unquestionably a good (though by no means perfect) boy, but as I have suggested, much of his virtue arises from his recognition that he is not inevitably good. When first-year students arrive at Hogwarts, they come to an assembly of the entire school, both students and faculty. Each first-year student sits on a stool in the midst of the assembly and puts on a large, battered old hat--the Sorting Hat--which decides which of the four houses the student will enter.After unusually long reflection, the Sorting Hat, to Harry's great relief, puts him in Gryffindor, but not before telling him that he could achieve real greatness in Slytherin. This comment haunts Harry; he often wonders whether Slytherin is where he truly belongs, among the pragmatists, the careerists, the manipulators and deceivers, the power-hungry, and the just plain nasty.
Near the end of the second book, after a terrifying encounter with Voldemort--his third: Voldemort had tried to kill Harry, and succeeded in killing his parents, when Harry was a baby, and Voldemort had confronted Harry again in the first book--Harry confesses his doubts to Dumbledore:
"So I should be in Slytherin," Harry said, looking desperately into Dumbledore's face. "The Sorting Hat could see Slytherin's power in me, and it--"
Harry is stunned because he realizes for the first time that his confusion has been wrong-headed from the start. He has been asking the question "Who am I at heart?" when he needed to be asking the question "What must I do in order to become what I should be?" His character is not a fixed, preexistent thing, but something he has responsibility for making; that's why the Greeks called it character, "that which is engraved"--the metal is capable of receiving and retaining a distinctive impression, but the impression once made is hard to erase.
In this sense the strong tendency of magic to become a dream of power makes it a wonderful means by which to focus on the choices that gradually but inexorably shape us into certain distinct kinds of persons. Christians are perhaps right to be wary of an overly positive portrayal of magic, but the Harry Potter books don't do that: in them magic is often fun, often surprising and exciting, but also always potentially dangerous.
"Put you in Gryffindor," said Dumbledore calmly. "Listen to me, Harry. You happen to have many qualities Salazar Slytherin prized in his hand-picked students...Resourcefulness...determination...a certain disregard for rules," he added, his moustache quivering again. "Yet the Sorting Hat placed you in Gryffindor. You know why that was. Think."
"It only put me in Gryffindor," said Harry in a defeated voice, "because I asked not to go in Slytherin..."
"Exactly," said Dumbledore, beaming once more. "Which makes you very different from [Voldemort]. It is our choices, Harry, that show what we truly are, far more than our abilities." Harry sat motionless in his chair, stunned.