"This", admits Fr Pat Ahern, "is way beyond the bishop's brief." "This" is the hall full of people arranged in various groupings which for a while interchange sequences of song and then, in a kind of choral meltdown, re-form as biblical characters. We are at one of the very many rehearsals for the Dance of Life production which will be mounted by the Kerry diocese in order to invest the opening of the third millennium with an appropriate symbolism. It was the idea of Bishop Bill Murphy, who introduced it to Fr Ahern as a suggestion for the formation of a celebratory diocesan choir. When Ahern invited the churches in the diocese to join, they all said "yes."

So then it grew. A script by Joe O'Donnell, whose work Pat Ahern had seen through Fr Dermot McCarthy, head of religious programming at RTE, was married to a score from Aidan O'Carroll, director of the Kerry School of Music and a former member of the Arts Council. This was further embellished by the choreography of Siamsa Tire's artistic director, Oliver Hurley. The circular nature of the enterprise is indicated by the fact that Ahern founded Siamsa Tire and was subsequently its artistic director for many years. Now retired, Ahern is more or less back where he started as a young curate, conducting a Gregorian choir at St John's Church in Tralee.

The enthusiasm of the people taking part in this project flows like a river of endorsement, but here and there an interpretative boulder causes a ripple, if not exactly a whirlpool. O'Carroll, for example, describes his commission as both challenging and inspiring. His work completed in six weeks "using a wonderful computer programme" and constructed on tonal building-blocks which allowed the incorporation of traditional Irish music as well as 20-part songs from the historical repertoire (although not necessarily much that would be found in the Veritas Hymnal).

These include, for the nativity sequence, an orchestral fantasy on the carol Diadem, which is no longer in general use, a Czech carol and In the Bleak Midwinter. The thrust is to find the inner, decoded simplicity to which people have responded through the ages. Thus, plainchant is the inspiration for a number of orchestral movements. The pageant begins in fact with a Hindu chant which - in another bigamous conjunction - is wedded to texts taken from the first chapter of John and the second of Genesis. Pat Ahern has a brother who is a Columban father in Fiji and he explains that the tri-syllabic "Om" chant represents the first sound, that of the divine.

What does a Hindu chant have to do with the millennium in Kerry? "Oh, nothing whatever", responds Pat Ahern, who knows already what I discover at the rehearsal: this low humming sound builds almost majestically to a unison in which the male voices demand that there be light and the sopranos answer that there was light. This fusion is strategically important: the sheer force of conviction dulls the instinct to question. The pageantry (largely the responsibility of the 50 seamstresses who work in a parish hall where the rooms are like caverns in which Aladdin might have stored the velvets and damasks and many-coloured coats required to clothe a thousand people, to designs by Molly Molloy of RTE) sweeps query into the background.

It returns, however, at the Siamsa Tire rehearsal where the lead dancers represent Christ as a second Adam and the Virgin Mary as the second Eve.

Gosh, is this orthodox? Oh yes, says Pat Ahern: St Paul has it, it is the thinking, yes, that as all men died in Adam, so all mankind is brought to life in Christ.

And Mary? We can't quite recover that reference, in fact, but Ahern says that theological nebulae of this kind strengthen such a presentation, allowing possibilities of interpretation which encourage attention. And anyway, there are two excellent dancers taking these parts and he didn't want to waste their dramatic opportunities.

Such consoling pragmatism reduces the threat of reverence in the production, and yet, having seen so many people of good will come together with varying degrees of difficulty (to Tralee from all over a far-flung diocese), to sing in four different languages - Irish, Latin, English and Hebrew - songs and choruses they have practised in their own churches, I felt the impact to be one of devotion. Something shared and unifying - the retired Church of Ireland bishop, Edward Darling of Ardfert and Aghadoe, is co-sponsor with Bishop Bill Murphy, and members of his congregation are also taking part - and also somehow solid.

"I would hope that it will be what it's intended to be," says Pat Ahern, standing in what is just another school hall, now permeated with a drained atmosphere of exhaustion yet still peopled with the outraged father of James and John, scolding the prophet who has lured his sons away and left him only abandoned boats and unrepaired nets. Also with a Barabbas who strides on with the self-righteous glamour of the freedom fighter, refusing to recognise the court; and with a Judas indignant at the historical weight of the part he must play if his master's destiny is to be fulfilled.

Here, as we talk about the £250,000 cost of the pageant and how it is to be met (half through ticket sales for the performances and the rest from sponsorship), a gorgeous John the Baptist awaits his cue, two teenage Marys giggle together and the prophet Simeon, appearing only once in the scriptures but now used as a kind of narrative continuum, stand ready to knit together the links between Old Testament and New.

Pat Ahern enthuses his singers once again to achieve that "hiss" which must last over two bars, please. They must emphasise again the word "hill" as Golgotha looms, they must hold for a beat the whisper "betray". The shrieks for crucifixion disintegrate into an almost animal pandemonium of hate, yet the tempo is contained within the priest's hands, the fingers opening and closing to control the rhythm. The alto line introduces a wistful "Ave Maria"; the solid tenors settle under the tenderly extended soprano phrases and, with the promise that they won't be kept beyond 10 p.m., just another school hall begins to quake with the emanations of salvation.

Dance of Life will be presented at 3 p.m. and 8p.m. at the Green Glens Arena in Millstreet on November 26th and December 3rd.