If you’ve never seen a play by Samuel D. Hunter, you’ll need to brace yourself for the emotional wallop of his latest gem, “A Case for the Existence of God.”

Mr. Hunter’s writing is that of a storyteller who never unnecessarily raises his voice, and his plays, usually set against a bleak Western landscape — among them “A Bright New Boise,” “The Whale,” and “Greater Clements” — follow the kinds of people whose voices largely go unheard outside of fiction. 

These aren’t typically the menacing outcasts you can find in the work of, say, Sam Shepard, to whom Mr. Hunter has been compared. They’re folks just struggling to avert despair, whose searching and suffering are documented with unpretentious authenticity, eloquence, and compassion — and, perhaps most miraculously, without cynicism.

For this first production of “A Case,” Mr. Hunter has a worthy partner in director David Cromer, whose flair for intimacy is ideally suited to a one-act piece that’s as quietly devastating as anything the playwright has delivered. Like most of Mr. Hunter’s previous efforts, “A Case” unfolds in his native Iowa — this time at the city of Twin Falls, in an office cubicle occupied by a 30-something mortgage broker named Keith.

Ryan, the play’s only other character, is also in his 30s, and the men have very young daughters who attend the same day care center. Less financially stable or knowledgeable than Keith, and engaged in divorce proceedings, Ryan wants to buy land he can’t afford so that he can build a house for himself and his toddler.

Although it seems at first as if “A Case” will focus on Ryan’s first consultation with Keith, it soon becomes clear that Mr. Hunter is intent on following the two men for a more extended period of time. Gradually and carefully, they reveal themselves to each other; we learn that Keith is gay, for instance, and that he’s facing a harrowing challenge to his parental status.

Keith is also black, and well-educated, from a prosperous family. Ryan is white, and grew up without the latter two advantages. Although their struggles are not dissimilar — both are terribly lonely, most obviously — and will bring them closer, their differences inform a tension that lingers. When Ryan tells Keith, “I think we share a specific kind of — sadness,” the statement seems at once perceptive and ironic. 

Arnulfo Maldonado’s scenic design places Keith’s small workspace in the center of a large and otherwise empty stage, reinforcing the characters’ mutual isolation and the vastness of the external forces weighing down on them. Under Mr. Cromer’s characteristically sensitive, penetrating direction, actors Kyle Beltran and Will Brill mine the stark realism, dry humor, and blazing empathy in Mr. Hunter’s dialogue.

Where lesser writers might have painted Ryan as either a dunderhead or a diamond in the rough, Mr. Hunter offers a predictably humane portrait of a man who found too little inspiration too late, and Mr. Brill’s performance in the role is painfully credible. Mr. Beltran is heartbreaking as the more patently self-conscious Keith, for whom love of any kind has always been elusive.  

Its title notwithstanding, “A Case for the Existence of God” doesn’t address religion or faith as directly as some of Mr. Hunter’s previous work. You won’t appreciate the title’s significance, in fact, until the breathtaking final moments — in which the playwright and Mr. Cromer, who have defied naturalism only in establishing the passage of time and the settings in which the characters meet, take an abrupt leap forward.

Being any more specific would require too big a spoiler, but suffice it to say that if your eyes aren’t burning by then or earlier, you should probably check your pulse. As a case for Mr. Hunter’s extraordinary talents, this softly piercing jewel of a play is bound to convert the uninitiated and fill believers with fresh wonder.