According to Gallup pollsters, 42 percent of Americans frequently attend Christian church services. Presumably, that figure is lower for contemporary playwrights, who often treat people of faith as confounding curiosities. There’s certainly a place on stages for new shows like Holly Down in Heaven (about a pregnant teen who refuses an abortion) and The Religion Thing (about an evangelical convert who mystifies her lapsed Jewish and Catholic friends). What’s refreshing about Bill Cain’s How to Write a New Book for the Bible, however, is its treatment of faith as a given circumstance rather than a plot device. And that starts with the protagonist being an ordained Jesuit priest.

Cain, not coincidently, is also a Jesuit priest. Yet there’s no proselytizing at Round House. This is a play about family that happens to be cloaked in religious vestments. Cain artfully borrows biblical metaphors and finds humor in insulting the scriptures. The Bible “begins with bad anthropology and ends with bad science fiction,” declares Bill Cain, the character, in the first act. Later he’ll note that Jesus may be the son of God, but he was kind of a lousy son. This is a well-written, eloquent play, fluidly directed by Ryan Rilette and engagingly acted by a quartet portraying the playwright, his brother, and their parents. The title is also the premise: Just as the Bible is composed mostly of epistles and accounts of familial dysfunction, the Cain family stories, interspersed with letters, could be a new chapter in a holy book. You make things holy, Cain notes, either by plating then with gold or covering them with shit.

Throughout the course of the play, he does a good bit of both. Gilded flashbacks to happier family times usually include a scene of his parents dancing, while the lowest moment finds the protagonist buying $100 of cleaning supplies because his mother has badly soiled the carpet. Cain began working on the play in 1993 after his mother died of cancer, and he wrote the very last scene first. It would be 18 years before it premiered onstage, however, and in the meantime, Cain, who also worked as a television writer, became a phenom for writing Equivocation, a groundbreaking play that explored Shakespeare’s closeted Catholicism. Garry Hynes directed the play off-Broadway in 2010, and in 2011 Arena Stage remounted the Oregon Shakespeare Festival’s premiere production.

How to Write a New Book marks Rilette’s directorial debut at Round House, and it’s a promising one. In lesser hands, this play could be a preachy, nonlinear mess. The main narrative follows Cain caring for his mother, but the play includes dozens of flashbacks, with Mitchell Hébert and Danny Gavigan, the actors who play his father and brother, adding levity when they pitch in to play hairdressers and doctors. At the center of the play is Ray Ficca, who depicts the playwright-priest without pretention or preciousness. If multiple endings draw the show out too long, that’s likely because in Cain’s memory, caring for a loved one with cancer is a long, drawn-out process. He also remembers those nine months as a time of relying on rituals and prayer, and on a sense of humor. For viewers, the spirit you’ll leave the theater believing in seems far from holy, but thoroughly human.