A prayer I wrote in response to Wednesday’s terror attack on Parliament has been shared more than 1000 times in 24 hours. The #Pray4london hashtag is trending worldwide. But does it make any difference? Is it anything more than a digital reflex - a collective gush of sympathy?

Julia Hartley-Brewer, a presenter on Talk Radio, certainly doesn’t think so: "Can everyone stop all this #Pray4London nonsense?" she tweeted angrily. "It’s these bloody beliefs that help create this violence in the first place."

I’m not quite sure how a belief in Jesus helped create Wednesday’s tragedy. Just yards from the attack, the words of the bible are inscribed in the floor of Parliament’s central lobby and for 158 years the chimes of Big Ben have spoken an hourly prayer over London: "Lord through this hour / Be Thou our guide / So, by Thy power / No foot shall slide."

There are four ideas which need challenging:

1. The idea that prayer is part of the problem

But perhaps Ms Hartley-Brewer is just meaning to say that religions in general fuel hatred and that the world would be so much more tolerant and peaceful if we would all just stop praying (cue John Lennon’s 'Imagine'). It’s true that most massacres are ideologically motivated and for some – such as Khalid Masood, who carried out Wednesday’s attack – those ‘ideals’ do indeed appear to be religious.

But for many others – such as Anders Breivik in Norway, or Mao Zedong in China, or Joseph Stalin in Russia, horrific aggression on a vast scale was motivated not by a religious paradigm, but by atheistic ideology. Ideas really matter, and ours are beautiful; rooted in ‘the Prince of Peace’, ‘the Comforter’, the ‘Healer’ who commands us to love and forgive our enemies.

2. The idea that prayer is irrelevant

In the UK today most people pray. Especially and understandably at times of personal or national tragedy. One government survey discovered that even among those who describe themselves as ‘non-religious’, 25% admit to praying at least once per month. We see this deep prayerfulness expressed in those DIY roadside shrines, in swelling congregations at times of collective trauma, and, yes, in hashtags too.

Instinctively we sense that tragedies demand more of us than mere sentiment. #Wish4London would not carry the same potency. The reality of both evil and good are revealed for all to see at such times. It suddenly seems obvious, even to the headline writers, that life really is a battle between terrible evil and brilliant goodness. Emerging from the mists of secularism we discover a religious landscape.

There is a desperate need in our world today for a deeper ecology, acknowledging that our social condition is not just political, genetic, economic and cultural, but also profoundly spiritual.

3. The idea that prayer is a distraction from action

As a church leader I am regularly criticised for calling people to pray at times of grave disaster. ‘Stop praying and do something to help!’ scream the trolls. It’s a viewpoint which presumes that people who pray don’t also ‘do something’. I would suggest that people who pray are far more likely to engage practically and politically as a result.

Many of the police officers, parliamentarians, nurses and doctors caught up in Wednesday’s attack are men and women of deep prayer. Several of them have been in touch with me personally to express their appreciation for the prayer support at such a horrific time.

Those of us who pray may seem like some strange, shrinking, irrelevant ‘other’ to certain members of the metropolitan media elite, but in fact we are here, we are everywhere, and we are engaged at the heart of the normal, rational world, trying to make a difference.

4. The idea that prayer is powerless

Many of the greatest parliamentarians of all time, from Cromwell to Wilberforce to Churchill were people of prayer who understood its power. King George VI published calls for prayer in every British newspaper, asking for God’s help in the liberation of Europe during the Second World War. There were extraordinary results, including at ‘The Miracle of Dunkirk’. Through enormous sacrifice the battle was won, on earth for sure, but also (as St Paul reminds us) in heaven, resulting ultimately in the overthrow of fascism and an end to bloodshed.

As we #Pray4London, perhaps we can claim the same promise sited by George VI on that occasion, "The Lord will give strength to his people: the Lord will give his people the blessing of peace." (Psalm 29:11) That surely is our prayer for those so suddenly bereaved, for those injured, for medics and pastors seeking to heal the hurt, for police officers protecting us and MPs leading us: "Lord, give us strength and bless us with peace." Amen.

Pete Greig is one of the leaders of the 24-7Prayer movement, the Pastor or Emmaus Rd, Guildford and the author of Dirty Glory.

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