There are many reasons why the West may be ill-equipped to fight against Islamism. We are afraid to get into another ground war in the Middle East; many of our armies and police forces are woefully under-resourced; we have no idea how to handle the sensitivities of Europe's Muslim population.

But if you want to understand the deepest reason of all, look no further than this week's controversy over the Church of England's Christmas ad . The 60-second video, which was going to be screened in cinemas before the new Star Wars movie, featured a diverse group of people reciting the Protestant Lord's Prayer. It was meant to show that "prayer is for everyone", but the Digital Cinema Media agency, which handles advertising for the leading cinema chains, banned it, explaining it could "cause offence to those of differing political persuasions, as well as those of differing faiths and indeed of no faith."

Now, as a religious person myself, I highly doubt that those of "differing faiths" will find anything offensive in this tame, non-coercive video. And if those of "no faith" are offended, they should develop thicker skin.

But, more importantly, it is an enormous mistake to erase religious expression from cultural and popular media when we are facing an enemy that is religiously motivated. Right now, we need to see and hear more about religion - not less.

The first step in defeating Islamism must be to develop a proper understanding of what it is, and what we're really up against. This is difficult, if not impossible to do, without understanding religion.

We’ve never had less insight into religion than we do today

Unfortunately, as a society, we have never had less insight into religion than we do today.

Nominally a Christian country, Britain is rapidly secularising, with a majority of our population (50.6 per cent) saying they have no religion at all, according to a 2014 British Social Attitudes survey. Of the minority who do have a religion, 56 per cent never attend religious services or meetings; less than a million people regularly attend CofE services on a typical Sunday.

In modern Britain, religious Christians risk being seen as eccentric.

Sure, we celebrate people of "other faiths" - Muslims, Sikhs, Hindus, Jews - but it's not really their faith we're interested in. We like exotic traditions that prove we're "multi-cultural". Is it any surprise, then, that large swathes of the British public struggle to understand what motivates Islamist terrorists? Our politicians insist that "this extremist ideology is not true Islam" (David Cameron, this week), and speculate that they are motivated by political grievances or criminality. They believe that if we leave the Islamists alone, they'll leave us alone, and that the "real" Islam is peaceful.

Because our society's understanding of religion is so limited, we find it inconceivable that people could be driven to mass murder, suicide and war in its name. We cannot grasp that a "real" religion might not always preach peace.

It is no coincidence that those who come from more religious societies - such as, for example, Abdel Fattah el-Sisi in Egypt, or the Christian wing of the Republican party – also want to take the hardest line against militant Islam. They understand the threat, because they understand how religious fervour can, in some cases, lead to fanaticism.

As long as British society continues to disdain religion, we are at a disadvantage in the war against terror. We don't need to agree with religion - much less practise it - but we do need to understand people's religious feelings.

We also need to be much more aggressive in showing that there are religious alternatives to militancy. The Lord's Prayer is a perfect example. The instinct to ban this piece of our national heritage will ultimately cost us dear.