I have been writing about Christians for more than 20 years now. I am married to one; I was brought up as one, more or less. Half a dozen of the most admirable, brave and honest people I know are Christians, and I don't think for a moment that I am either smarter or better than they are. If I am right, and they are wrong, this is due to no great merit on my part. It is certainly not because I am less prone to illusion than they are, or more firmly attached to the truth. I know I can generate quite enough illusions of my own without supernatural help.

These aren't mere preliminary throat-clearings. They are a deep and important part of the reason why I think the world would be a worse and poorer place if Christianity were to vanish from it, even though, as I say, I am not a Christian myself. Why not?

I was brought up in a household that took religion seriously. My father, who had spent his childhood in Belfast, regarded Christianity as important but wrong. One of his earliest memories was of being pushed to the floor of a tram which was running down a street with the Protestants on one side shooting through the windows at the Catholics on the other and – ecumenically – vice versa. He still went to church in his official capacity as a diplomat, but he never for a moment supposed that a grownup could take the doctrine seriously. It had not been his observation that the meek inherited the earth or any significant part of it. Nor have I seen as a journalist anything to prove him wrong.

My mother felt that belief was noble, church attendance a duty, and Christian ethics compelling, but she couldn't, so far as I know, believe that the story was actually true. I was sent to schools with compulsory chapel, which I disliked, though I loved the prayer book and rhythms of the King James Bible. I still do. When I was about 13, I sat a scholarship exam to a second-rate public school, and got one on the strength of what was called the "divinity" essay. This was my first real moment of doubt. I remember looking at the piece, after 45 minutes of frantic scribbling, and thinking "This is very good; very powerful. But I don't have the faintest idea of whether any of it is true"; and it seemed to me that the chaplain who praised it couldn't have any idea either.

Later in my adolescence, I discovered Jung, Robert Graves and The Golden Bough on mythology and Bertrand Russell's essays; Aldous Huxley and LSD for high-minded mysticism. As a result, I thought myself far above any narrow little doctrines such as Christianity. I would have said then that I was spiritual, but when I grew up a little more, I came to repudiate all that kind of romanticism in favour of a grim and rationalistic sobriety. I read Gibbon and lots of Karl Popper. I came to believe that we had a duty not to believe in miracles. At the same time, I came to appreciate and to some extent understand the psychological realism of Christianity. The fact of original sin still seems to me one of the most obvious and important things about human nature, even there was no garden, and no Adam, nor an Eve. I can't believe in physical resurrections, but psychological ones keep people alive.

When I became a religious affairs correspondent, and started to meet Christian intellectuals, I came to realise that some at least believed nothing I found abhorrent or ridiculous. They no more take the Bible as a work of history than I do. There were some with whom I could and can talk seriously in the confidence that we understand the world in almost exactly the same light and see it disfigured by the same shadows. It would be wrong and invidious to name living people, but the late Lord Runcie was one of the most admirable men I have ever known, and if Jesus was good enough for him that's a powerful argument.

Yet still I won't join. In need only reread some parts of CS Lewis to know that if that hectoring certainty is right, I would rather be wrong. Most of the bishops I have known have been a sorry lot. It is hard to believe that they are right about anything much and I would certainly not wish to associate myself with the modern Church of England and all its squalid vanities. I left the 1998 Lambeth Conference determined to do nothing which might have me mistaken for a Christian. No doubt the feeling is mutual. This wouldn't matter if they were representatives of a great tradition. But I find I can't believe in the tradition, either. Looking at what Christians have actually believed about the world, and the ways that they have in practice understood their doctrines, I know that almost every Christian now alive would have been considered a heretic 500 years ago; and that the witch-burners of the 17th century would themselves have been heretics 500 years before.

For similar reasons, I can't accept the intellectual authority of the Roman Catholic church. Calvinism, while it it intellectually satisfying, is emotionally repugnant to me. In the end, I suppose, my objections to God are, as they must be, theological: the workings of divine providence are just a little too inaccessible to human reasoning. The problem of suffering remains insoluble. There is no possible theodicy. But I can't, either, take the Dawkinsian view that the problem of suffering is an illusion generated by the illusion of God. You can't mend the heart in a heartless world by observing that the world is in fact heartless. That's not the point.

I suppose I end up saying that I accept the Christian account of the problem; I just can't accept Christianity's account of the solution, and so I remain, by the grace of God perhaps, an atheist.