The real date of Jesus' birth was almost certainly not on December 25. But this date has special resonances, says Biddy Collyer.

In darkness, the choir process down the aisle carrying candles; a lone voice sings, 'Once in Royal David City' and so Midnight Mass is celebrated in churches, and cathedrals all over the country late on the evening of December 24. Christmas - the birth of Jesus, the Christ child. Only is it?

There is no mention in the Bible accounts of the actual day of his birth. There was no register that would have noted it and that census would more likely have happened at one of the three great Jewish festivals, none of which fall then. The shepherds could not have been sitting out their cold vigil in December as their flocks were safely gathered into folds by November.

Working from John's gospel account, if Mary's 'Boy Child' was conceived at the time her cousin Elizabeth was already three months pregnant with John the Baptist, and cross-referencing this to Elizabeth's husband Zechariah's priestly turn in the Temple, then the end September or early October is the likely time. It was the time when the Jewish community celebrated their release from slavery with the Feast of Tabernacles by living outside in booths or tents. When St John talks about Jesus 'dwelling with us' he uses the Greek word for tent.

So, if the circumstantial evidence can be mounted up for autumn, why do we 'Decorate the Halls with Holly' on December 25? Pragmatic politics, that is what is was. On that day, the Romans celebrated the birth of the Sun God, and it also coincided with Saturnalia, another pagan feast around then. With the Christianisation of the Roman Empire in the fourth century, these feasts continued, and were gradually subsumed into our Christmas Day.

It may be the wrong date but I don't think there is any going back on this. I can't see us buying Christmas trees and decorating them in the autumn. And, when I think about it, what I am celebrating is the light of Jesus coming into our dark world. It fits somehow. (Not Down Under of course, where it's full summer and hot.)

Some children are frightened of the dark and sleep with the light on and it's true that just a small light dispels the darkness. The light of a fire comforts. An outside light draws us down the path to the house.

And that's why the opening verses of John's gospel resonate so strongly with its many references to the light, obliquely yet clearly talking of Jesus as the Light of the World, culminating with, 'The true light that gives light to every man was coming into the world.' Who wouldn't rather walk in the light than remain in the darkness?