Although I've read quite a few of C.S. Lewis's works, I'm not personally familiar with any of the Harry Potter books, so I'll simply proffer this excerpt from an article by John Andrew Murray for discussion among those who've read both Lewis and Rowling.
. . .What about Narnia?
Christian fans of Harry Potter insist that the series is no different than C.S. Lewis' The Chronicles of Narnia, a series that many Christian parents accept.
It is true that both authors create fantasy parallel worlds involving young British children who encounter magical creatures. Both develop admirable characters and evil villains. But this is where the comparison ends.
The difference between the two hinges on the concept of authority. From a Christian perspective, authority and supernatural power are linked.
Take a look at Mark 2, where Jesus heals a paralytic. When Jesus first sees the paralytic, He says, "Son, your sins are forgiven." This sets up the following scene:
Now some teachers of the law were sitting there, thinking to themselves, "Why does this fellow teach like that? He's blaspheming! Who can forgive sins but God alone?" Immediately Jesus knew . . . that this was what they were thinking . . . and He said to them, "Why are you thinking such things? Which is easier: to say to the paralytic, ‘Your sins are forgiven,' or to say, ‘Get up, take your mat and walk'? But that you may know that the Son of Man has authority on earth to forgive sins. . . ." He said to the paralytic, "I tell you, get up, take your mat and go home." He got up, took his mat and walked out in full view of them all. (Mark 2:6-12)
Christ's power flows from His authority. That's the nature of all legitimate power — it is granted and guided by authority.
When we read Rowling's series, we find that she effectively divorces power from authority. There is no sovereign person or principle governing the use of the supernatural.
Magical power is gained through inheritance and learning. It is not granted by a higher authority, because there is no higher authority — at least none higher than Harry's mentor, Albus Dumbledore, and the evil Lord Voldemort. The two are equal, antagonistic and unaccountable to a higher authority.
In Narnia, power and authority are welded together. That authority is Jesus, in the character of the great lion Aslan — creator and sovereign ruler of Narnia, son of the Emperor Beyond the Sea. Good power is power that is bestowed by Aslan and exercised in accordance with his will. This good power is at work when the children Peter, Susan and Lucy use gifts bestowed on them by an agent of Aslan.
Evil power, on the other hand, is power that is seized or conjured — rather than bestowed — and exercised for selfish ends. Those who resist the temptation to use such power are commended, as was Digory, in The Magician's Nephew. But those who wield it (such as Jadis, also in The Magician's Nephew) and the White Witch (in The Lion, the Witch and the Wardrobe) are eventually vanquished by Aslan.
Despite superficial similarities, Rowling's and Lewis' worlds are as far apart as east is from west. Rowling's work invites children to a world where witchcraft is "neutral" and where authority is determined solely by one's cleverness. Lewis invites readers to a world where God's authority is not only recognized, but celebrated — a world that resounds with His goodness and care.
It's a difference no Christian should ignore.