When the Resurgam Choir and Camerata Kilkenny perform their 'authentic' version of Handel's Messiahthis week, the audience may be in for a few surprises, hears Arminta Wallace

We love Handel's Messiah here in Ireland. We always have, ever since we nicked it from under the nose of our neighbours in the middle of the 18th century. Handel was going through a bad patch in the 1740s: changing fashions in Italian opera, plus the fact that rival opera houses in London were at each other's throats, had made his musical life in that city something of a misery. He was on the point of going back to his native Germany when his friend, Charles Jennens, came up with a cocktail of beautiful biblical texts and offered them - along with the use of his elegant country house - as the basis for a piece of sacred music.

It was an offer Handel couldn't refuse. He set to work, and wrote the whole thing in 24 days. And then he disappeared with the finished score. Or, as the somewhat baffled Jennens put it in a letter dating from September 1741: "I heard with great pleasure at my arrival in Town, that Handel had set the Oratorio of Messiah; but it was with some mortification to me to hear that instead of performing it here he was gone into Ireland with it . . ."

And so it was that Dublin, rather than London, hosted the premiere of Messiah in the spring of 1742 as part of a series of charity concerts at Neale's Musick Hall on Fishamble Street. We all know the story about how advance interest in this historic performance was so lively that gentlemen were asked to come without their swords, and ladies without hoops in their skirts, in order to squeeze everyone in. What we tend to forget, however, is that the hall was quite small to begin with - as was the orchestra, a modest band led by Handel himself from the organ, and the choir.

The intimacy and excitement of that opening night is what Resurgam and Camerata Kilkenny aim to recreate this week when they perform Messiah in three of Ireland's most beautiful sacred spaces: St Patrick's Cathedral, Dublin; St Nicholas's Church in Galway; and the Holy Trinity Cathedral in Waterford. It will be what is now called an authentic, or period, performance, with the Camerata Kilkenny orchestra, led by Maya Homburger, playing baroque instruments, and the singers of Resurgam well-schooled by conductor and baroque expert Mark Duley in period performance style.

This is not, as some people might imagine, a simple matter of lighting a few candles and decking the musicians out in curly wigs. It's a whole different mindset, as Resurgam baritone Sean Green explains.

"It's not just a matter of 'here come the good old tunes'," he says. "It's a matter of treating the piece as a real work of dramatic art, from those quite solemn opening bars to the final amen. It's rather like a stage play or an opera or a feature film, in which everyone has an important role to play. Even - especially - the audience."

From this perspective, Handel's much-performed masterpiece is no tame Christmas turkey.

"People come along expecting to get into the Christmas spirit," Green adds. "So they're a bit jolted, in a way, when we launch into part two and it's not angels singing and it's not peace on earth - it's 'Behold the Lamb of God', and it's about suffering. Some of the choruses would be in keeping with Bach's St John Passion and the anger that's unleashed in that part of the New Testament."

It's quite a challenge for a relatively small number of musicians to carry off Handel's lengthy and technically demanding work, which many audiences associate with the massed choirs and full-sized orchestra of recent tradition. But the pay-off from period performance, says Constance Gardiner, who sings alto in Resurgam and who is also - in another musical life - a violinist and violin teacher, is immense.

"It's very much a chamber situation," she says, "with the orchestra so close to the choir that it's almost inside it. It gives you a real, physical connection with whichever instruments are playing the line that you're singing - and of course the speeds in baroque performance would be slightly faster, at least in the faster movements, so it can be really exhilarating."

That's a verdict with which Caroline Senior, of Garter Lane Arts Centre in Waterford, would concur. The city's Cathedral of the Most Holy Trinity has been extensively refurbished - as has Barronstrand Street just outside, which is now pedestrianised - making it the perfect venue for a baroque Messiah.

"It was built by the baroque architect, John Roberts," she says. "It accommodates up to 1,000 people very comfortably, and yet has the intimacy of an amazing space to work in."

Last time Resurgam came to town, Waterford had not had a performance of Messiah since 1954, and the church was packed to the rafters in suitably Handelian style, though hoops and swords presumably weren't a problem.

"It was fantastic," Senior recalls. "The Resurgam Messiah is light, stylish and effervescent and full of interesting details. They put the trumpet up in the organ loft, and it was wonderful watching the audience react - where on earth is it coming from? . . . It was such a thrilling evening that afterwards I nearly kissed the bishop. But I refrained."

The famously grouchy Dean of St Patrick's Cathedral in Dublin, Jonathan Swift, would have approved of such restraint. He was reluctant to allow his choristers to take part in the premiere because he disapproved of men singing in such secular establishments as Neale's Musick Hall in Fishamble Street. He was eventually persuaded when the organisers agreed to make a donation to local mental hospitals. This charity fundraising aspect has itself become part of the work's history, and has helped precipitate its shift in the musical calendar from Easter performance dates to predominantly Christmas ones.

Over the past few years, there's also been a fashion for casting a counter-tenor rather than a contralto in Messiah performances, as Resurgam soloist, the English counter-tenor Owen Willetts, confirms.

"I've got a bumper crop of Messiahs this year; 10 altogether," he says. "I look forward to them, although I do think the soprano gets the best arias."

Added to the distinctive sound of baroque instruments, the unmistakable timbre of the counter-tenor adds yet another subtly different shading to the period soundscape. But does Messiah sit comfortably for the counter-tenor voice?

"It varies from person to person," says Willetts. "It certainly does for me. In some places it's a bit low, but then contraltos find it low as well."

Willett's favourite aria is But Who May Abide the Day of His Coming?, which, he says with evident satisfaction, "has a very beautiful melody, and then a fire-and-brimstone middle section".

But then, everybody has his or her favourite Messiah moments. For Constance Gardiner, it's that final, rip-roaring Amen, "not because it's the end, but because you can really let go during that one".

For Sean Green, the passage He Has Borne Our Grief and Carried Our Sorrows has special resonance. "As a really small boy I sang in my church choir in Belfast," he says. "And although they weren't able to handle - ouch, sorry - the whole Messiah, we always did sing this passage at Easter, and I think it's a very moving part of the overall work."

On a high-tech note, it's interesting that the most frequently downloaded Messiah chorus from a recording available on iTunes is not - as one might expect - the rather bombastic Hallelujah chorus, but the celebratory Unto Us a Child is Born. Despite its reassuring familiarity, therefore, there's clearly lots more to learn about this much-loved choral work.

"Every year that we perform it, we uncover more things," says Green. "With smaller musical forces you can unpack layers that aren't really obvious when you hear it performed by 150 singers and an orchestra of 40. To my ear, there's a certain freshness and brightness that comes with baroque performance. You can hear how nimble and agile the music is."

• Resurgam and Camerata Kilkenny, conducted by Mark Duley, will give three performances of Messiah with soloists Lynda Lee (soprano), Owen Willetts (counter-tenor), Daniel Auchincloss (tenor) and Raitis Grigalis (bass) in St Patrick's Cathedral in Dublin tonight, at the Collegiate Church of St Nicholas in Galway tomorrow, and at the Cathedral of the Most Holy Trinity, Waterford, on Fri. All performances are at 7.30pm