It's quite a view. Whether or not you like modern art, this is surely one of the most memorable sights you'll see here at the Tate Modern. You'll hear people say, 'You can see everything – St Paul's, the sweep of the river, the City, the Globe Theatre...

We quite like big views, big pictures – theories about the world that solve all the problems, apparently simple plans that are going to put the whole thing into proper perspective once and for all. But 'everything' is just what you don't see from up here.

Come downstairs, right down to ground level: here is what the big picture doesn't show you, the shadow side of the stunning view up at the top. Behind the Tate is this exhibition of children's art – art by children whose entire experience has been abuse, violence and poverty.

These are the things that are out of sight so much of the time – here in Britain or elsewhere in the world: a reality we usually try to spare ourselves. But the children involved – the children from devastated homes and communities in the United Kingdom, the children living in fear or poverty in other countries, homeless because of war or disaster, and we're all still trying to come to terms with the shock of what's happened in South Asia in the last few days – they can't turn it off when it gets uncomfortable. This is life, this is normality for them.

This exhibition, called Shrinking Childhoods, is organised by the charity Kids Company, who give emotional and practical support to vulnerable children. Camilla Batmanghelidjh is the founder of Kids Company.

The big picture doesn't always help, if it takes our eyes off these local, individual stories. Someone said about the slaughter of the Jews in the death camps, 'It isn't six million dead; it's one person dead, times six million'. You could be overwhelmed by that; you could feel there was no hope or faith possible.

But our Christian faith talks about a God who isn't content with the big picture. In Jesus he comes alongside us as a human being; he shows that he is a God always involved with people one by one. And that's why this exhibition is the really important story here.

These children and teenagers have somehow been given the confidence to face the horrors they live among, and think about them, make something of them, challenge all of us to do what can be done to confront these things and make them less likely to happen. The people who run the work that lies behind this exhibition take them one by one and give them something of the love and trust they haven't known; and miracles happen.

These records of suffering may test your faith. But listen to the children here, to their hopes and their pride and their appreciation of how they've been cared for and it will test your doubt. In the small details of each life, something extraordinary is happening, something is changing.

So as we think about the coming year, let's not spend all our time on trying to perfect the huge plans that will change everything. We ought to be asking, 'What's the difference I can make to this situation, this person, to myself, to someone close, to someone whose face I know?' The biggest picture we could ever hope for is the sight of what the human heart is capable of when complete love and trust are allowed to touch it. Think global, act local, they say: what's the difference only I can make, however small, here in this place at this time.

A Happy New Year to you all. God bless you.

© Rowan Williams 2004