You can learn a lot about the art of the sell from watching TV evangelists, says actor Gus Murray.

"They're a bit like the swan on the water – very graceful and very smooth but the legs are kicking like crazy underneath," Murray says. "People see the confidence but they don't see that they are working really hard. I'm quite in awe of what they do, speaking for half an hour or more with no script, and making it look like it's just coming to them."

Murray is speaking ahead of his starring turn in Miracle City, an upbeat musical-theatre satire written by the late Nick Enright and inspired by the scandal that engulfed the best-known evangelists of colour TV era, Jim and Tammy Faye Bakker.

Murray has been studying the preacher's art. "There is that folksy tone of voice that is so endearing and open," he says. "There are the fluid hand gestures to illustrate gentleness and love and that exaggerated humility. These people are huge TV stars and their churches are rolling in cash but they present as humble with this 'aw shucks' vibe. I'm trying to weave all that into the man I portray."

First produced in 1996 by Sydney Theatre Company, Miracle City takes the form of a live-to-air Christian TV show hosted by southern evangelicals the Truswell family: Ricky and Lora Lee, their born-into-the-business children, Bonnie Mae and Ricky-Bob, and their rafter-raising gospel trio The Citadel Singers (Missy Higgins, Lara Mulcahy and Josie Lane).

The Truswells have a mission to fulfil: the building of a Christian theme park, a place for the faithful to play and pray. All they need is the money – and lots of it.

Kellie Rode plays Lora Lee Truswell. "At first I was looking at Tammy Faye Bakker and that was helpful," Rode says. "But more current for me is Victoria Osteen."

Osteen, Rode says, is the glamorous wife of the Texan "prosperity church" pastor-mogul Joel Osteen. "She's interesting because most of her speeches aren't overly religious. Most of what she does is more like motivational speaking and some of it is very powerful. I think that's why she has such a wide reach. She's not saying you'll go to hell if you do this, or that you'll go to heaven if you're good. She's just trying to inspire you."

People like Osteen clearly love the limelight, Rode says. So does Lora Lee. "I see her as a very true person. She's not out to mislead anyone. But she enjoys the camera and she loves the attention. She comes from a place of wanting to help people but after a while it becomes about the money and power. There are major comprises that need to be made."

Miracle City was first revived at the Hayes Theatre Company in 2014. This production, staged at Sydney Opera House, is new and realised by a completely different team under director Darren Yap.

"I saw the Hayes production and it was great," Murray says. "But the great thing about this show is that there are so many other choices you can make. We can all bring our own energy and thoughts to it."

Murray adds that it has enormous appeal for those audiences who don't regard themselves as musical theatre fans. "I know people who find music theatre a bit twee sometimes when people sing their feelings and their thoughts. Miracle City isn't like that. The music is beautiful and joyous but it's also part of the TV show. It's incredibly clever."

Miracle City plays in The Studio, Sydney Opera House, October 12-29; from $59, sydneyoperahouse.com