Throughout history, cults of all sizes and shapes have created exciting dramas to spread their doctrines to the uninitiated. Many of the same elements we see in comic books, paperback SF and fantasy novels and Hollywood movies were first introduced in these stories, not as entertainment per se, but as literal propaganda, meaning as messages designed to 'propagate the faith'.
Street performers and vendors selling refreshments, icons and amulets would cluster around outside, adding to the carnival atmosphere. Kind of like the Dragon*Con of their day.
Besides his "best-seller" Dianetics, Hubbard would advertise his cult with a sci-fi novel entitled Battlefield Earth. Following L Ron's death, celebrity Scientologist John Travolta would use his post-Pulp Fiction clout to stage a big budget adaption of the novel, which would go down in Hollywood's ledger book as one of the worst movies ever made.
Think about this when you turn on your TV tonight. Cults aren't always theological, they're just as often political these days. Or 'scientific'. With the kind of big salaries we used to see receding from the mass media, people go into documentary film-making especially to propagate their own beliefs, or better yet, the beliefs they've been trained to believe are their own.
UPDATE: Pedro at our Facebook group, The Lunar Barbecue (see right column) recommends Metamorphoses aka The Golden Ass by Apuleius. It's one of the oldest surviving novels, it's based in the old Roman Isis cult, and it's a work of magic unto itself. It's also hilariously funny and surprisingly easy to read. Check it out, either online or from the library.