Biblical figures and ancient characters often fight the forces of evil through God-inspired power. Moses spoke with God, deriving a power from the Holy Word that would allow him to part a sea. Jesus turned water into wine and consulted with long-departed prophets. In so doing, Jesus unites his message of goodness with the ancient traditions of His people. In ancient literature, Odysseus conferred with the dead to gain their wisdom and find his path. Again, I'm not saying that Odysseus equals Christ, but all of these heroic figures from the past share certain important traits. I find it very ironic that the very people who criticize Potter on the grounds that it is non-canonical praise tales like the Odyssey, the Aenid, the tales of Arthur, or the Lord of the Rings; the Potter books deal with many of the same issues as do these heroic tales.
Rowling definitely builds on ancient myth and biblical precedent. Like the young Arthur, Harry is chosen to fulfill a prophecy and to lead others to greatness. Like Arthur who is drawn to a sword meant only for him, Harry has his special wand that will help him defeat evil. Like Odysseus and Aeneas, Harry must travel far to claim his place in a world that is at times dangerous and even deadly. Like the young Arthur, Harry learns that the world is not always what it seems. People betray and disappoint. Arthur is betrayed by his queen and his first knight. Harry learns that his parents and his teachers are human, prone to frailty and pettiness as well as courage. Like Tolkien's hobbit heroes and their band of warriors, Harry and his friends must face the enemy and forge their destiny. Each of us is set on a path with pitfalls and battles to be faced. Harry and his friends also are an unlikely band of warriors. They are wizards, but they are also kids wearing jeans and T-shirts. Kids identify with them because they are Everyman, armed with magic. Many have read Tolkien's work as a metaphor for his own experiences in the Great War. The young people who fought that conflict, like the hobbits, were also unlikely heroes, but they, too, faced the enemy with courage.
What I say to skeptical parents is that Harry Potter follows an ancient tradition that hopefully will ignite their children's imaginations, encouraging them to read the source material from which it derives. Because of Little Women, I read German philosophers like Kant and Fichte. Because of the Beatles' lyrics, I read King Lear and Lewis Carroll. Because of Godspell, I read the Bible. The Harry Potter books stand on their own, but they also can send children on a treasure hunt in which they discover the source of the magic. Don't discount "popular culture."