...I think the problem is that so much of the religious
right failed to see the Christianity in the Potter novels because it knows so
little Christianity itself. Yes, there are a few ‘memory verses’ from Saint
Paul, and various evangelical habits like the ‘sinner’s prayer’ and the alter
call. However the gospel stories themselves, the various metaphors and figures
of the Law and the Prophets, and their echoes down through the past two
millennia of Christian literature and art are largely unknown to vast swaths of
American Christendom, including its leaders.
Let's right up front get rid of any notion that what the author is referring to is a phenomenon of evangelical Protestants only. Catholics are every bit as guilty of being ignorant of Christian heritage, and as our Christian heritage forms the bulk of our Western heritage, one could argue secularists are guilty as well.
People used to grow up hearing the Bible, even if they weren't particularly religious, and we also lived in a culture where it was okay to mention religious themes in conversation or artistic expression and so people gained some familiarity almost through their skin. That is gone. We don't know the Bible and we don't know expressions originating there.
For example, John Derbyshire once mentioned using the expression "being expected to make bricks without straw" and having not one of the group of educated Americans he was talking with know the term. As another example, I once referred to Isaac and Ishmael and the lifelong churchgoer I was talking to asked who they were. Kathleen Norris has written about her hymnal changing the term "my Ebenezer" to "my greatest treasure", presumably because people nowadays aren't expected to know what Ebenezer refers to. And lest it seem I'm only picking on other people, back in the nineties I had to ask someone where the phrase "through a glass darkly" came from. I wasn't a Christian, but considering what our Western heritage is, that is no excuse. I didn't know any Ebenezer other than Scrooge, either, and while I assumed it came from the Bible like so many old-fashioned names, I didn't know who the Hezekiah my busdriver was named for was.
And taking my examples away from the Bible itself, I can remember as an older child reading a magazine my mother sometimes got at church (I read everything...well, except the Bible) and seeing an article in which the author mentioned attending Handel's Messiah. I'd never heard of the Messiah, I'm not sure I'd ever heard the term messiah, and I don't think I was aware of any classical music having been informed by Christianity. Yet I was more culturally literate and well-read than any of my classmates. And, at least through the elementary school years, my religious education was the equal of any of theirs. I may have read lots of novels and plays and recognized lots of paintings and sculpture, but there was any number of things I didn't know about the Christianity I'd supposedly been raised in and even when I recognized something came from the Bible or was a religious concept I often couldn't tell you what the reference was or define the concept.
Is any of this important? Well, when as a teenager I was told by various sources that Christianity hates life and regards the natural world as evil, I believed it because I was too ignorant to know otherwise. That mental path--or chute--was already well-greased by years of media depictions of Christians as ignorant hicks who were apt to be bigots as well and I'd already long since rejected Christianity, but that one particular lie which I did not have the knowledge to refute, more than anything else, resulted in my becoming a pagan. So is it important for people to know what Christianity teaches? If you're a Christian parent who doesn't want your teenager to leave Christianity for something else, I think you'd say yes.
And as to Christian history--or the general history of those parts of the world formerly known as Christendom--and the artworks inspired by Christianity, you do not have to be Christian to believe it is important to know about those. Friar Tuck, the Holy Grail, the Nun's Priest, the fleur-de-lys, the Pieta, De Profundis, and Judith Beheading Holofernes belong to all of us.