"It did come as a pleasant surprise," she says with a smile that is rare and possibly reserved for special occasions such as this one.

The Paranjoti Academy Chorus is to perform 18 carols before the congregation in the old Mumbai suburb of Bandra, of which three were sung at the Rashtrapati Bhavan. "You've come at a good time," she tells us. "Look we're all dressed up and ready to sing!"

The group is an assorted bunch of Parsis, Hindus and Christians -- two of them, you notice, aren't even Indians. Katja Kohl is a German exchange student studying at the University of Mumbai and Ben Davis is a London-based researcher currently in the city on an assignment.

Kohl and Davis, however, were part of the contingent that travelled to New Delhi. The former has been with the choir for a few months and says that she missed out on the opportunity because 'only 30 of us were granted permission to go'. "That would've been some news back home," she says "Me dressed up in a sari, singing for a choir before the President of India!"

Videos: Hitesh Harisinghani

The Paranjoti Chorus, however, has generated enough curiosity amongst the local news gatherers. At least two other cameras are hovering around the altar -- one of them belongs to the BBC.

Wadia doesn't seem to care much for the spotlight. Halfway into the service, she sternly asks one of the camerapersons to switch off the light.

Significantly, the choir performs So Jaa Re, one of the three carols that were sung before President Pratibha Patil. It is a lullaby in Hindi composed by Abel D Cruz, a former member of the choir and arranged by Coomi Wadia.

Of the rest, one is the popular Deck the Halls while the other is a Marathi composition called Madhura Madhura, arranged by Nariman Wadia.

Katja Kohl seems to know the lines of the Hindi and Marathi carols like the back of her hand. Never once do you see her miss a syllable, even as she occasionally refers to the lyrics written for her in the Roman script. "We were also given the translation of the lines," she tells us later. "So I actually knew what I was singing!"

Video: Hatish Harisinghani

Kohl also looks just as much at ease performing Madhura Madhura as she is singing O Tannenbaum, a German ode to the Christmas tree.

At the end of each carol, Wadia takes a bow. Every once in a while she invites a member who has been the heart of a particular piece to share the dais with her.

Ben Davis' turn will be at the very end, when he plays the church organ as an accompaniment to the last two carols. His fingers move swiftly over the keyboard, his feet in conjunction with the harmony.

Already a few enthusiastic members of the congregation have begun to sing. They will get their chance too, when Wadia invites everyone to join in. Soon the entire church is singing in one voice. Joy to the world echoes in the air and soon even the shyest of the lot join in.

Indeed, the spirit of Christmas is universal. Wadia, who worships Zarathushtra and sings in churches across the world, would stand testimony to this.

Video: Hitesh Harisinghani

For those interested in attending, the Paranjoti Chorus will also perform at the All Saints Church at Mumbai's Malabar Hill on December 21 at 7.30pm, and at Afghan Church in Colaba, Mumbai, on December 22 at 7.30pm .