Britain has once again suffered the fury of a terrorist attack – the third in under three months, the second in only 10 days. Innocent people were slaughtered by conscienceless men in the name of a perverted ideology. They used a vehicle as a weapon, then pulled out knives and stabbed people. According to one witness, they were shouting 'This is for Allah.'

At the time of writing, seven people have died and 48 have needed treatment in hospital. The terrorists have been shot dead.

Today is Pentecost Sunday, when churches up and down the country have been looking forward to celebrating the birthday of the Church. It's a time of rejoicing and hope, marking the coming of the Spirit on the waiting disciples. No longer would they be powerless bystanders in a drama taking place elsewhere. They would be Spirit-filled actors, moving and shaping the world in the power of God, bearing witness to the crucified Christ, preaching and demonstrating love and forgiveness to a harsh and brutal world.

Up and down the country pastors and preachers will think about what to say and how to respond. How can they preach on a joyful Pentecost in the light of another manifestation of the powers of darkness? Today is also the culmination of the Thy Kingdom Come initiative from the Church of England, when hundreds of thousands of people have been praying for conversions. Large-scale events are taking place in cathedrals and parks, in which the keynotes are hope and confidence for the future. How can they continue?

How can they not?

Around 500 years ago, Martin Luther wrote a great hymn, whose first line is 'A mighty fortress is our God'. The times were far more violent and dangerous than our own, and they were to get worse. But the hymn was still sung, as a statement of faith and hope. Luther cast it as a straightforward battle between good and evil; between God and the 'ancient prince of Hell'. It's not fanciful to see a manifestation of the demonic in what happened last night, and in the Manchester Arena, and on Westminster Bridge – and what's happening in Iraq and Syria, and in the other troubled places of the world. There is an overbalance into evil, and we shouldn't be reluctant to say so.

But now if ever is the time to pray, 'Thy Kingdom Come' and to trust in God for the future. Now is when the Church needs the Pentecostal fire to fall and empower us for witness. There are grieving people to be comforted. There are many others who are angry and bitter, and who want to take revenge against people who carry the same religious label, but who have absolutely nothing in common with the perpetrators of this act.

It's in the darkest times that we have most need of light. So may God enlighten us and empower us, and may his Kingdom come.

Follow Mark Woods on Twitter: @RevMarkWoods