NEW YORK – Certainly the strangest if most original musical to arrive in many years, “The Testament of Ann Lee” tells the true story of the British woman who founded the American celibate Christian sect the Shakers.

Amanda Seyfried, an Oscar nominee for playing a 1930s Hollywood legend in “Mank,” jumps back to the 18th century to shake and sing with every bit of her being as Ann Lee.

Critics have responded to Mona Fastvold’s biopic which details Lee’s adventurous, often traumatic life and the musical sequences where the Shakers are ecstatically inhabited by the spirit.

“Apparently, Ann Lee had a beautiful voice, but she wasn’t perfect,” Seyfried, 40, said in a post-screening discussion. “She was singing her feelings, and she was connecting to something totally inside herself. And outside of herself. In order to find any sense of peace.

“She chose the light as opposed to the dark. And with that passion, love and devotion, whatever sound comes out is beautiful! Because it’s coming from such love.

“So, I didn’t have to worry about how I sounded so much. Mona had me laying on the floor of the studio when we were in Budapest trying to figure out where we might go when we were shooting.

“Because we hadn’t shot it yet, anything was possible. At one point I was on the floor and I wouldn’t even sing it. I’d scream.

“They didn’t use most of that. But then I got to do it live as well. So I was just exploring every possible feeling. And we left nothing on the table.”

Budapest was where “Testament” filmed.  But, as Seyfried noted, “I also had the luxury of time and space with all that preparation for dancing, because Celia Rowlson-Hall, who’s the incredible choreographer, lives upstate. So we would rehearse for weeks across from the donut shop.

“I worked really hard. I hate dancing,” she confessed, “but I understood this wasn’t ‘dancing.’ It was movement.

“And again, it’s all holy. It’s all devotion. It’s all based in this (expletive) desperation to be loved. So when you think about that, although it’s very technical — doing the accent, singing and the dancing — if you’re scared of it, you understand where it all is great!”

As the Shakers’ leader, Ann Lee espoused celibacy; a response to the four children she had who all died in infancy. Without sex in their marriage her husband left her.

“That’s the beauty of honoring something that really, truly happens — and destroys people. Because (the loss of her children) destroyed her, and that’s why she became leader of the biggest utopian society in American history. Because it came from something so traumatic.”

“The Testament of Ann Lee” opens Friday

Director Mona Fastvold. (Photo Marius Hauge/Courtesy Venice Film Festival)