The photographs that stay with us, haunt us, are always those of particular faces: one mother's grief, one child's nightmare bewilderment and loneliness. Last week, we learned in Canterbury of the death in the Asian disaster of a 14 -year old from the King's School, with her mother and grandmother. And because of that, people here experienced what had happened in a different way. The number of deaths horrifies us - but what most painfully reaches our feelings is the individual face of loss and terror.

In 1966, when the Aberfan disaster struck, I was a sixth former beginning to think about studying theology at university. I remember watching a television discussion about God and suffering that weekend - with disbelief and astonishment at the vacuous words pouring out about the nature of God's power or control, or about the consolations of belief in an afterlife or whatever. The only words that made any sense came from the then Archbishop of Wales, in a broadcast on Welsh television. What he said was roughly this: "I can only dare to speak about this because I once lost a child. I have nothing to say that will make sense of this horror today. All I know is that the words in my Bible about God's promise to be alongside us have never lost their meaning for me. And now we have to work in God's name for the future."

He was speaking from the experience of losing one child; but he was able to speak abut a much greater tragedy simply because of that, not because of having a better explanatory theory. "Making sense" of a great disaster will always be a challenge simply because those who are closest to the cost are the ones least likely to accept some sort of intellectual explanation, however polished. Why should they?

Every single random, accidental death is something that should upset a faith bound up with comfort and ready answers. Faced with the paralysing magnitude of a disaster like this, we naturally feel more deeply outraged - and also more deeply helpless. We can't see how this is going to be dealt with, we can't see how to make it better. We know, with a rather sick feeling, that we shall have to go on facing it and we can't make it go away or make ourselves feel good.

The question: "How can you believe in a God who permits suffering on this scale?" is therefore very much around at the moment, and it would be surprising if it weren't - indeed, it would be wrong if it weren't. The traditional answers will get us only so far. God, we are told, is not a puppet-master in regard either to human actions or to the processes of the world. If we are to exist in an environment where we can live lives of productive work and consistent understanding - human lives as we know them - the world has to have a regular order and pattern of its own. Effects follow causes in a way that we can chart, and so can make some attempt at coping with. So there is something odd about expecting that God will constantly step in if things are getting dangerous. How dangerous do they have to be? How many deaths would be acceptable?

So why do religious believers pray for God's help or healing? They ask for God's action to come in to a situation and change it, yes; but if they are honest, they don't see prayer as a plea for magical solutions that will make the world totally safe for them and others.

All this is fair enough, perhaps true as far as it goes. But it doesn't go very far in helping us, one week on, with the intolerable grief and devastation in front of us. If some religious genius did come up with an explanation of exactly why all these deaths made sense, would we feel happier or safer or more confident in God? Wouldn't we feel something of a chill at the prospect of a God who deliberately plans a programme that involves a certain level of casualties?

The extraordinary fact is that belief has survived such tests again and again - not because it comforts or explains but because believers cannot deny what has been shown or given to them. They have learned to see the world and life in the world as a freely given gift; they have learned to be open to a calling or invitation from outside their own resources, a calling to accept God's mercy for themselves and make it real for others; they have learned that there is some reality to which they can only relate in amazement and silence. These convictions are terribly assaulted by all those other facts of human experience that seem to point to a completely arbitrary world, but people still feel bound to them, not for comfort or ease, but because they have imposed themselves on the shape of a life and the habits of a heart.

Most importantly in this connection, religious people have learned to look at other human faces with something of the amazement and silence that God himself draws out of them. They see the immeasurable value, the preciousness, of each life. And here is one of the paradoxes. The very thing that lies closest to the heart of a religious way of life in the world, the passion about the value of each and every life, the passion that makes religious people so obstinate and inconvenient when society discusses abortion and euthanasia - this is also just what makes human disaster so appalling, so much of a challenge to the feelings. Sometimes a secular moralist may say in contemporary debates: "Nature is wasteful of life; we can't hold to absolute views of the value of every human organism." That is not an option for the believer. That is why for the believer the uniqueness of every sufferer in a disaster such as the present one is so especially harrowing. There are no "spare" lives.

That is also why the reaction of faith is or should be always one of passionate engagement with the lives that are left, a response that asks not for understanding but for ways of changing the situation in whatever – perhaps very small – ways that are open to us. The odd thing is that those who are most deeply involved – both as sufferers and as helpers – are so often the ones who spend least energy in raging over the lack of explanation. They are likely to shrug off, awkwardly and not very articulately, the great philosophical or religious questions we might want to press. Somehow, they are most aware of two things: a kind of strength and vision just to go on; and a sense of the imperative for practical service and love. Somehow in all of this, God simply emerges for them as a faithful presence. Arguments "for and against" have to be put in the context of that awkward, stubborn persistence.

What can be said with authority about these terrible matters can finally be said only by those closest to the cost. The rest of us need to listen; and then to work and – as best we can manage it – pray.

© Rowan Williams 2005