The problem with the person who drove a lorry into a crowded market of Christmas shoppers wasn’t that he was too religious, but that he wasn’t religious enough. It was the action of a half-believer, the sort of thing done by someone who doesn’t so much believe in God – but rather believes in the efficacy of human power exercised on God’s behalf, as if God needed his help. As Rowan Williams once put it: “For the person who resorts to random killing in order to promote the honour of God, it is clear that God is not to be trusted. God is too weak to look after his own honour and we are the strong ones who must step in to help him. Such is the underlying blasphemy at work.”

It’s a very basic point. The truth of God’s existence does not depend on me. It does not depend on me filling my church with believers at midnight mass. Nor does it depend on me (or anyone else) winning or losing arguments about God’s existence on Twitter. God is not like a political party that lives or dies on its support or lack of it.

The man who shot the Russian ambassador to Turkey shouted “Allahu Akbar” – that God is great. If he really thought that, he wouldn’t have shot the ambassador.

This may seem obvious, but there is an insidious unspoken theological heresy to which religious professionals like me are sometimes drawn, in which God is seen somehow to depend upon my effort, and that it is my task in life to keep people believing because it is people believing that sustains God’s very being.

How does this connect with terrorism? Consider the conclusion that the American scholar Jessica Stern came to after conducting numerous interviews for her book Terror in the Name of God: Why Religious Militants Kill. “The point of religious terrorism is to purify the world of corrupting influences,” she explains. “But what lies beneath these views? Over time, I began to see that these grievances mask a deeper kind of angst and a deeper kind of fear. Fear of a godless universe.”

Religious terrorists feel that God is under threat. And it’s their mission to save him – from unbelief, from false religion etc. That, of course, has things totally backwards. We don’t save him, he saves us. And moreover, he saves us by persuading us that it’s not all about us.

“The great aim of all true religion,” wrote William Temple, “is to transfer the centre of interest from self to God.” Religious terrorists don’t get this because they still think it’s all about them, and what they can achieve. That’s the heresy. The man who shot the Russian ambassador to Turkey shouted “Allahu Akbar” – that God is great. The thing is, if he really thought that, he wouldn’t have shot the ambassador. His mistake was to think that God was somehow dependent on, and grateful for, his violent assistance.

Indeed, what Allahu Akbar surely means (and Arabic speaking Christians use the phrase too) is that God needs nothing from me in order to be God. And when this is recognised, I can (sometimes with quite considerable relief) drop all my desperate schemes and arguments that try and keep him going in the face of opposition and disbelief. Indeed, in order to seek to transfer the centre of interest from self to God, to achieve other-centredness, you can’t make it all about you, your spiritual struggle, your religious heroism.

But all this is contrary to the standard narrative the government employs about so-called “extremism”; namely, that the problem with religious terrorists is that they are too religious. The implication of the theologically illiterate Prevent strategy, for instance, is that if religious people were a bit less religious they would be a lot less dangerous.

But as Jonathan Swift famously explained: “We have just enough religion to make us hate, but not enough to make us love one another.” Which is why I want religious people to be more extreme in their faith, not less; to put aside their own boiling inadequacy and to trust in God’s greatness and that he knows what he is doing.

Moses and Jesus and Muhammad were all extremists. They trusted in God over their instincts. And the shorthand for this is Allahu Akbar – a phrase the terrorists will never understand.