Christmas is coming and there's nothing we can do to stop it. We know it's coming because the lights are already up, the trees are in, and because three doors on the advent calendar have been opened. We know it's coming because the prophets of anxiety are predicting a difficult time for the shoppers and retailers of our over-stretched, debt-ridden land.

We feel the imminence of Christmas in the mincemeat sensations of excitement and dread; of wishing it would never end and wanting it over with now. Of the need to be at home – with family and friends – and the desire to escape it all and get as far away as possible.

As the Grinch in Dr Seuss' story says:

'Christmas! It's practically here!'

...Then he growled with his fingers nervously drumming,

'I must find a way to keep Christmas from coming!'

Advent means the arrival – or coming – of an important person or thing. Yet break it down into its compound words: 'ad' and 'vent' and it looks alarmingly like something to do with advertising and windows – it sounds like a big commercial wind. Which of course it is, has been, and probably always will be. Which is why Grinchlike, seasonal rants about the commercial aspect of Christmas will do nothing to change it.

Priests asking us not to throw out the baby Jesus with the bath salts should save their breath. If they want us to question anything at Christmas it should be the baby: Do we need the baby? Do we want the baby? What is this baby for? It's easy to see that Christmas 'doesn't come from a store'... easy to guess 'it means a little bit more'... the question for us all is: What?

Isaiah, a prophet who lived before Christ, framed our need in this way: 'O that you would tear open the heavens and come down.'

There was an ache for a saviour long before one appeared. As to what this saviour is for, Isaiah put it in these startling terms: 'For those living in darkness, a light has come,' and later 'he will be pierced for our transgressions and by his wounds we are healed.'

For Isaiah it took 600 years and a thousand advent calendar windows before the double doors opened on the baby in the manger he predicted would be 'the saviour of the world.' That's a kind of patience – a kind of expectation and waiting – that's hard to grasp.

In theory, for us, the waiting is over. The baby – whether we like it or not – is here – Immanuel or God with us. As the Grinch discovered, we can't stop Christmas from coming, 'Somehow or other, it came just the same!' The challenge for us this advent is finding the space to think about why it came at all in the first place.

An extract taken from 'Godbothering', the new book from novelist and broadcaster Rhidian Brook out now from SPCK.