It will be a century this coming summer that the great Protestant theologian Karl Barth began his revolutionary commentary on St Paul’s Epistle to the Romans. A quiet and studious man of simple tastes, Barth was an unlikely revolutionary. He listened to Mozart, smoked his pipe and read the paper: “Theology is done with the Bible in one hand and the newspaper in the other,” he said. But mostly he sat and wrote. His Church Dogmatics is more than six million words. And no, I haven’t read it all. But his considerably shorter Epistle to the Romans, written earlier, was the decisive turning point in 20th-century theology. It was a book that dropped a bomb on the comfortable assumptions of German liberal thought. And it’s a bomb that needs dropping again – but this time much closer to home.

Which brings me to David Cameron’s message of Christmas cheer, that we are a “Christian country”. Given the rapid decline in the number of church-going Christians, and given Cameron’s sketchy relationship to faith, what he probably meant is that we are a Christian culture; that the ethos of Christianity is woven into the warp and weft of British institutional life. Oh, what a slippery word “ethos” is – Christianity in homeopathic doses. Barth would not have approved. For what is frittered away in this mutually back-slapping accommodation between faith and the state is the ability of the church to stand up to the state’s propensity for war. Indeed, the point of saying that Jesus is Lord is to say that Caesar isn’t. Neither Caesar nor his armies nor his civilising institutions. Which is why Christians should always call time on their religion being used as a deodorant to mask the stench of war and death.