Stephen Sondheim’s rarely produced musical “Passion” is being revived this month at Boston Court Pasadena, guided by Artistic Director Emeritus Michael Michetti. Set in 1860s Italy, it considers love, lust and obsession through the triangle of virile army captain Giorgio (Richard Bermudez), his beautiful lover Clara (Bryce Charles), and a mysteriously ill woman named Fosca (Meghan Andrews) who upends Giorgio’s romantic notions about love and awakens him to the broader world. The original 1994 production won Tony Awards for Best Musical, Best Score, and Best Book (by James Lapine).

Compared to Sondheim’s best-known musicals — “Company,” “Into the Woods,” “A Little Night Music,” “Sunday in the Park with George,” “Sweeney Todd” — “Passion” is unusually personal, almost raw with sensuality and longing. Sondheim began composing his rhapsodic score after seeing Ettore Scola’s neoromantic 1981 film “Passione d’Amore” (which was based on Iginio Tarchetti’s 1869 novel “Fosca”). The show opens with Clara and Giorgio making love and singing “Happiness,” exchanging a line that foreshadows Giorgio’s later friendship with the traumatized Fosca: “How quickly pity leads to love.”

Bryce Charles, who delivered a show-stopping performance as Sarah last year in Pasadena Playhouse’s production of “Ragtime,” acknowledges that Sondheim’s music is “harder than most scores.” But it also provides wonderful material for actors, challenging them to “sing in a way that tells the story” via his precise structuring of melodic lines.

“I almost call it a play,” says Richard Bermudez, who is onstage virtually the entire time, “because it reads like a play that happens to have music.” Indeed. With no space allowed for applause, and no intermission, dramatic tension mounts within the musical’s cloistered setting until Fosca and Giorgio wrap their voices around a question for the ages in “Finale”: “Why is love so easy to give/ And so hard to receive?”

“The joy is that it is absolutely stunning. I have loved this music for a very long time,” Charles says, adding that loving it from afar is not the same as truly understanding Sondheim’s luxurious melodies and exacting rhythm changes from within.

“As beautiful as it is to sing, we kind of wanted to just fast-forward to it being easy and free and be able to live in the music. But that’s not the way any show goes, especially not an obscure Sondheim piece,” she says. “You have to dig deep into the music and learn everything note by note and then really let your body feel it.”

Charles says it was “comforting” to learn this production is being done with new orchestrations for a chamber ensemble. The smaller scale better serves the material’s intimate nature, and should “really invite the audience into the story.”

The more nuanced arrangements challenge Bermudez, who is accustomed to belting out big, vocally gymnastic roles in musicals like “Evita” and “Jesus Christ Superstar,” to pull back and sing as though he were speaking conversationally.

“My normal instinct is to be singing toward the back of a 2,000-seat theater, and this is a 98-seat theater and it’s gotta be as honest and heartfelt as possible,” he says. “There’s nothing performance about it. We’re not using body mics. There’s a certain realness to hearing a voice unamplified, unaltered, without an electronic device — you forget what that feels like. It’s going to be a real interesting experience for the audience.”

Sondheim fans should be pleased to learn that Bermudez is singing “No One Has Ever Loved Me,” a poignant number not always included in previous productions. The song arrives at a critical plot juncture, but if not approached carefully it can disrupt the show’s finely balanced tone.

“Part of the reason no one ever does ‘Passion’ is the material is very challenging; it’s one of Sondheim’s most cerebral scores,” Bermudez notes. “And the subject matter, if not handled tactfully and carefully, can be off-putting because people can mistakenly take it as a ‘Fatal Attraction’-type theme, and it’s not that at all. It’s about learning that true beauty is not skin deep, and learning to accept someone for their inner beauty, regardless of what their outer trappings may be. It’s a beautiful idea, but a very difficult point. … Sondheim is challenging us to think about what it means to love someone truly.”

Love’s contradictions are mirrored in the evolving relationships between characters. To Charles, “Passion” offers validation that love can be genuine even if it doesn’t last in its original form.

“A lot of times we walk through life and think we know what we want, who we are,” she muses. “Based on where we are in life in that moment, someone may seem appealing, and then we grow and maybe our counterpart doesn’t grow in that same way. When that happens, there’s the question of, Was our love true then? Was it valid, was it real? I think the answer is yes. Was it meant to last through eternity? No.

“Some people come in your life for a lifetime and others for a season. All of those love experiences are valid. That’s something that the show is expressing.”” 

“Passion” previews at Boston Court Pasadena, 70 N. Mentor Ave., Pasadena, 8 p.m. Thursday-Saturday, March 5-7, 2 p.m. Sunday, March 8, and 8 p.m. Thursday, March 12, then officially opens Friday, March 13, and runs through April 19; $25-$55. Info: (626) 683-6801.