Year after year, church attendance at Christmas continues to defy the trends. Disconcerted clergy find themselves putting on an extra carol service or Christingle. Cathedral Deans start worrying about health and safety regulations as the number of people standing at the back is still growing five minutes before the service starts. And in spite of all the high-profile anti-God books published this last year, I suspect it's not going to make much difference to these swelling numbers in church over Christmas.

So what's going on? I don't think it's that people's doubts and uncertainties are all magically taken away for a couple of weeks in December. But once in a while people need a chance to face up to the bits of themselves that they cheerfully ignore most of the time – a chance to notice what might be missing in their lives.

And Christmas gives us just this. It gives us a story to listen to. It gives us a sense that what matters most deeply to us matters to God too. And it gives us a moment of stillness in a more and more feverish environment.

It gives us a story. If you go to a carol service, you'll notice that it isn't just about the story of Jesus' birth. It starts right back at the beginning of human history and tells us that everything started well and then everything went wrong, and we got so tangled in habits and attitudes that trapped us and damaged us that we couldn't get out again.

So the question stares us in the face – 'Is this your story?' Did you start well and then find yourself snarled up in things that drain your life and energy?'

There won't be many people for whom that doesn't ring a bell or two. And then the story goes on to say something quite strange and surprising. God steps in to sort it all out. But he doesn't step in like Superman, he doesn't even send a master plan down from heaven. He introduces into the situation something completely new – a new life; a human baby, helpless and needy like all babies.

And it's by that introducing of something new that change begins to happen. Like dropping a tiny bit of colouring into a glass of clear water, it starts to affect the whole glassful. The Christmas story doesn't try to explain how it works. It just says, 'Now that this story, Jesus' story, has started, nothing will be the same again.'

So we're not being asked to sign up to a grand theory – just to imagine that the world might have changed. And most of us can manage that for a moment or two. Christmas lets us hold on to that for just a bit longer.

And it tells us that what matters to us matters to God. Most of us have deep-rooted instincts about all kinds of things – about our families and children, about the need for fairness and forgiveness, about honesty and faithfulness in private and public. A great deal of the world we normally live in seems to ride roughshod over many of these instincts. We get panicky about what our society seems to be doing to marriage and families, about the forward march of a technology that doesn't ask the moral questions, about the cynicism and brittleness of a lot of political talk and the celebrity culture.

Christmas reminds us of a God who is completely committed to the weakest, who uses power only so that human life can be fuller, more peaceful and generous, who gives us the help we need to make our relationships stable and faithful - and who requires of us a complete honesty about ourselves, and gently, steadily chips away our self-deceptions. Christmas tells us that our best instincts about human nature and what's needed for a healthy world and society aren't just things we've made up. They are rooted in the way the whole universe is shaped by God.

Often people demand 'moral leadership' from religious figures. Confession time: like others, I suspect, my heart sometimes sinks when I hear this, and I think, cynically, that it's just about people wanting religious leaders to tell them they're right.

But there's more to it than that: it's not that folk simply want bishops or vicars to lay down the law all the time. But they do want sometimes to be assured that their hopes aren't empty and their fears aren't stupid, in a world where things change so fast and so disturbingly. They want to know that there is a 'home' for their feelings and ideals, that the universe has a shape and a purpose. And yes, religious leaders will be failing in their job if they can't meet this need.

But as I've hinted, it's not just a need for words. It's a need for space where you don't have to struggle, to fight for your place at the table. You're just welcome for who you are. It's a bit of a paradox. We usually spend the weeks before Christmas in a feverish nightmare of anxiety and driven busyness, as if we were going to celebrate the festival by making our normal situation even worse! But then there comes a moment when we really have to take time out if we're going to stay sane. That's the moment when people start thinking about church.

We still have this half-buried conviction that church is a place where, at least at this time of year, we ought to be able to feel at home. We turn up, tired and overwrought, perhaps, still thinking vaguely about what we haven't done and need to do before tomorrow. And then the story unfolds. Yes, this is our story, and yes, we can for a moment believe that this birth makes a difference. Yes, God cares about the kind of world we want to see and his faithful love is the basis of what makes a really liveable life. And no, we don't have to do anything for this time except take it in. There are no entrance qualifications. The door of Jesus' stable is open and anyone can come in and sit down.

None of this – I can hear the atheist protesting – means it's true, surely? Not in itself, no. But it suggests that, if God is a 'delusion', as some would like us to believe, then quite a lot more of our human life is a delusion as well, including many of our deepest values and our hopes for forgiveness and peace. All sorts of things will make up your mind about whether it is true or not – and naturally I want people to believe it is and I'm happy to have the arguments. But you will never understand why it might matter for it to be true unless you can take in what the Christmas story is saying to us about who we are and the world we live in.

So – arrive early! There are millions who still want to ask these questions and hear the story. And there are millions for whom it's not just a piece of our 'heritage' – a stately home we might visit – but a place to live. God is for life, not just for Christmas.

Every blessing to you all for a very happy Christmas.

© Rowan Williams 2008