Many Irish women believe that their sons can walk on water, but Mary the Mother of God’s son literally did. It made for a remarkable life, regardless of whether or not you believe in it.

Next week Irish actress Fiona Shaw, 54, will be channeling both the love and fury of the most famous woman of all time when she steps into the title role of The Testament of Mary, the remarkably powerful new play by award winning Irish novelist and playwright Colm Toibin, when it opens in previews on Broadway.

At first glance Mary may seem like an unlikely subject for Toibin, originally from Enniscorthy, Co. Wexford, but look again and she follows easily from the central themes of his most recent novel, Brooklyn – both stories feature women asserting their identities in an era and in an atmosphere that’s usually hostile to their efforts.

It’s impossible to refrain from speculating about what made Toibin, a former altar boy raised in a Catholic home where the rosary was said, approach his famous (and famously elusive) subject. Lives of Jesus are often attempted by celebrated writers but Mary, he concedes, has been consistently overlooked.

“Maybe it’s because they feel her life is so well-known,” Toibin tells the Irish Voice. “She suffers but she doesn’t speak, she’s meek and mild.

“As opposed to Jesus on the cross who says quite a lot, he has parables and sermons, he has a lot to say and so do the gospel writers. Growing up I noticed how her silence gave her power. I didn’t notice particular devotion to Saint Matthew, Mark Luke or John.”

The Testament of Mary is not, it should be noted, the work of a militant agnostic or atheist out to prove or disprove anyone's theories, his own or anyone else's. Instead it's a remarkably powerful – and at times terrifying – attempt to grapple with the reality of the woman who inspired it. But it not a Molotov cocktail delivered to the crisis-plagued church.

“We would have said the rosary at home,” says Toibin, recalling the utterly unremarkable Irish religious traditions of his youth with obvious affection.

“The first connection our house had with the wider continent of Europe was via Lourdes. People came back talking of the heat, the different habits, people didn’t put milk in their tea, all the strange things that happened in France – you couldn’t get fizzy orange.

“But in the evenings they were in the grotto. All of that was a part of my life.”

In a staged rehearsal with Shaw on Broadway last week to introduce the play, the spine-tingling fury that accompanies Mary's recollection of her son's terrible fate came to the fore early. I ask him if he was surprised by the intensity of Mary's anger as he wrote the play?

“No, because if you’re writing that it’s not a question of technically getting it down on the page. It’s a question of actually inhabiting it,” he says.

“It’s the only way the voice will come. If you give yourself the feeling first and then see what words come. That was the way it came.”

Toibin admits that didn’t plan the play out in detail, although he did have in mind how it would go.

“When I was starting I intended that the Lazarus story, who Jesus raises from the dead, would be a small part, there would only be a glancing reference to it. Then I found that when I wrote it, it had taken pages. Of all the stories, of all the miracles, this is the one that is awe-inspiring.”

In performance Shaw memorably recreates the moment, as Mary watches her son raise a man from the dead. But to be dug out of the earth and reborn, in the sight of many, having been buried for days and left behind is, when you think about it, utterly terrifying.

Toibin recreates Mary's awe, and the crowd's awe, but he also notes that Lazarus does not speak, nor seems to know where he is, and the wonder turns to quickly to profound dread. It makes for electrifying theater.

“Any time you write a novel or fiction, it’s just an idea that someone had. Your job is to find the detail and see where that takes you,” says Toibin.

“That would include attempting to wonder and then try and write down what it might have been like if someone had told you that story and everyone around you believed it. So she has to listen to it, and she remembers it in great detail.”

In Toibin's play Mary has not ascended in to heaven. In fact she's under a kind of house arrest as the men who are writing the gospel interrogate her about every detail of her past. She’s being guarded and protected for her own good, but they pointedly need her cooperation.

“They’re attempting to put shape on what happened and to her, it was chaotic and won’t ever be otherwise. If you’re writing fiction you’re always aware that you’re putting a shape on something,” Toibin says.

“The way it was experienced might have been different. The drama that's going on in this text is between her efforts to be truthful and their efforts to be influential.”

It wasn’t always clear that this religion would hold such a place in world history, even in the first 50 years after the crucifixion, Toibin says. It took extraordinary determination on the part of a number of people and organization skills for this story of life, death and the good news of resurrection to move as it did.

“I’m catching it at a moment when it is not clear what it will do. When it may be a cult or a sect that will fade,” he says.

“It’s a key moment when a number of men have seen the possibility of spreading the good news, and a woman on the other hand has not seen that possibility. She simply remains traumatized and for her it is a simply unresolved personal experience.”

Often Toibin’s Mary is closer to Medea than the Bible's silent lady in blue, but this is intentional. Toibin knows that her son, the figure on the cross, has extraordinary mythic power, as does the idea of his life being a kind of an intervention in world history. At all points he focuses the play on what it must have cost her to witness her son’s suffering.

“All I want to do is to allow her to take it personally, as anybody might. I think it’s vital that she speaks without being interrupted,” he says.

Before she was anything else, Toibin reminds us, Mary was a girl, then a wife and mother. Her story unfolded over time; it was not known to her beforehand.

Even what the gospels tell us about the angel and the virgin birth, they don’t raise the vale on the terrible final act. She went through her life putting one foot in front of the other, and grappling with what happens, as we must all do.

It was the landmark productions by Galway's Druid Theatre, directed by Garry Hynes, that actually persuaded Toibin that he could write The Testament of Mary, he says.

“Once it occurred to me that it could be done I became interested. That came from looking at the work of Garry Hynes at Druid, looking at the work that Siobhan McKenna, Marie Mullen and Fiona Shaw and Deborah Warner were doing,” he offers.

“Those plays had an enormous effect on me and the audience.  I realized that theater was the place where this work could be done.”

Both Shaw and the play's director Warner have a way of making a text matter to an audience, where you walk out of the theatre transformed, Toibin says. That was why he wanted to work with them.

Meanwhile, production on the big screen adaptation of Toibin’s last novel Brooklyn is moving ahead, but he won't be involved with the effort he says.

“Nick Hornby wrote the screenplay based on the book which is great. Technically and emotionally it’s a brilliant piece of work. He has stripped the story to its essentials and I’m very happy with his work,” he says.

“As far as I understand Rooney Mara has agreed to do it. No one needs me any more!”

(The Testament of Mary opens at the Walter Kerr Theatre, 219 West 48th Street, New York, on March 26. Call 212-239-6200 for tickets and showtimes.)