"Christianity's just a man-made religion."

We've all heard it said, and more than once. Behind it is the thought that the strange beliefs Christians hold, the peculiar rituals we take part in, are all products of human imagination. Like other cultural phenomena – art, law, education, technology – religion is a human product.

The thing is, we know that.

No thinking Christian is going to deny that religion in general – and the Christian religion, since that's what we're talking about – is the product of human imagination, thinking and effort. It couldn't be anything else, since it's what humans do. Humans write books, sing songs and pray prayers. We build churches and cathedrals and organise ourselves into denominations and sects. It can't be any other way.

But the implication goes further than that. Why should we bother to take it seriously, since God is obviously 'made up'? And that's where we part company with our critics.

First, the fact that something is 'made up' doesn't mean that it shouldn't be taken seriously. Religious systems are like other systems: they arise to meet certain needs. The fact that religious belief of some sort is found in every culture implies that it's hard-wired into us, psychologically or socially or both. It's true many people – especially in Europe – seem to get on fine without it, but even in the UK, there are millions of believers who find their faith gives shape and meaning to their lives.

Why does religion "work" for so many people? That depends on your point of view. Stephen Hawking, an atheist, has described religion as "a fairy story for people afraid of the dark". On the other hand, Oxford Professor of Mathematics John Lennox has described atheism as "a fairy story for people afraid of the light". Pay your money, take your choice.

It's possible to explain religion in terms of its social usefulness (it helps bind communities together) or as a means of social control (priests act as reinforcers of government power) or as a way of making hard lives more bearable (it is "the sigh of the oppressed creature, the heart of a heartless world, and the soul of soulless conditions", as Karl Marx put it).

And none of those things are wrong, because religion is a human construction. You can look at how it functions and see all those things at work.

But what Christians say is that Christianity has developed to be what it is because it corresponds to something real. We may have 'made it up', but that's because we are responding to something which has been given to us – 'revealed', in Christian terms. Our belief that God, in some mysterious but profound way, 'looks like' Jesus comes from our sense that He is too far beyond us for us to be able to imagine him in any other way than as a human being.

There's something like this thought in the Old Testament, in the prophet Isaiah's great tirade against idol-worship (only, of course, without Jesus). He imagines a craftsman chopping down a tree, cooking his meal and keeping himself warm with part of it and making a god with the rest. "Shall I bow down to a block of wood?" he asks (44:29).

It's tremendous stuff. He senses God is more than any human representation of him can encompass and calls people to a deeper understanding. What he doesn't acknowledge, though, is that the idol-maker, too, has his spiritual urges. He isn't doing religion well, but he's trying, as all people of faith try. And you can either see all religion as just people carving gods out of bits of wood, or you can go with St Augustine, who said: "You have made us for yourself, and our hearts are restless until they find rest in you."

As a Christian, I believe God has revealed himself in Jesus and that the Bible is a faithful witness to him. Criticisms of 'religion' don't worry me in the slightest.

Follow Mark Woods on Twitter: @RevMarkWoods