The movie treatment of his novel, “Angels and Demons,” is cleaning up at the box office this week. The sequel to “The DaVinci Code,” due out in November, might buoy the publishing industry through the recession. And if you want to understand the state of American religion, you need to understand why so many people love Dan Brown.

It isn’t just that he knows how to keep the pages turning. That’s what it takes to sell a million novels. But if you want to sell a 100 million, you need to preach as well as entertain  to present a fiction that can be read as fact, and that promises to unlock the secrets of history, the universe and God along the way.

Brown is explicit about this mission. He isn’t a serious novelist, but he’s a deadly serious writer: His thrilling plots, he’s said, are there to make the books’ didacticism go down easy, so that readers don’t realize till the end “how much they are learning along the way.” He’s working in the same genre as Harlan Coben and James Patterson, but his real competitors are ideologues like Ayn Rand, and spiritual gurus like Eckhart Tolle and Deepak Chopra. He’s writing thrillers, but he’s selling a theology.

Brown’s message has been called anti-Catholic, but that’s only part of the story. True, his depiction of the Roman Church’s past constitutes a greatest hits of anti-Catholicism, with slurs invented by 19th-century Protestants jostling for space alongside libels fabricated by 20th-century Wiccans. (If he targeted Judaism or Islam this way, one suspects that no publisher would touch him.)