When the memorial to the victims of the 7/7 bombing was announced, I thought it was a mistake. Not because I begrudged the money spent on it, or thought it would be unhelpful to the victims' families; it clearly wasn't. I just thought it was too soon. I don't claim any particular prescience here, but it was obvious then that the struggle against Islamist terrorism would last for decades. There would be more attacks, more deaths and more pain. There would be more memorials.

That there have been so few terror-related deaths on UK soil since then reflects two things: the tactics of the militants, who have largely concentrated their efforts elsewhere, and the vigilance of the security services. However, the 7/7 anniversary falls as we are still coming to terms with the Sousse attack, in which British citizens were deliberately targeted. The terror threat is not over yet, or anything like it.

After each attack, I find myself asking the same questions. What is the point? What did it actually achieve? And the answer is always the same: absolutely nothing. If the terrorists want anything, it is what no government could possibly grant. British policy in the Middle East will not change one jot because British people die in terrorist attacks. That's not how it works. On any strategic assessment, these attacks are utterly pointless.

And here's the thing. Terrorism rarely works. Yes, you can find examples of places where it's contributed to making territory ungovernable: Jewish terrorist attacks directed against the British Mandate in Palestine, for instance, or any number of pro-independence movements in post-war Africa and elsewhere. But where there's a minority of fanatics attempting to overthrow the settled will of a majority population: no.

However, this isn't about strategy: it's about something much more primal. It's about revenge, a deep identification with 'them' rather than 'us' and a desire to make people who have inflicted harm suffer in return. This identification is on the basis of religion. That's weird, when most deaths and dislocations in the current Middle Eastern conflicts have been inflicted by Muslims on other Muslims. It's also deeply immoral: there's no pretence that those who died or were injured on 7/7, or in Sousse, were personally involved in British Middle Eastern policy. They died at random, because they were British.

So what do they want? They want us to suffer, as they suffer. They want us to enter the same world of corrosive hatred and impotent rage that they inhabit. They want to make a hell in Britain to match the hell in Syria. They want us to be like them.

After 9/11 in the US, American attitudes to Muslims shifted sharply toward the negative. It would be foolish to deny that non-Muslim British attitudes have remained unchanged because of what's happened since, both in Britain and elsewhere. But here's another thing: terror attacks by Muslims haven't succeeded in making us hate Muslims. We know the difference between the jihadis who think it's OK to cut people's heads off and the ordinary folk who are our neighbours and friends. It's the difference between the Ku Klux Klan and your local parish church.

And that's the other reason why the terrorists won't win: they can't make us hate. They can make us grieve and they can make us afraid, but they can't make us hate if we choose not to.

But there's another layer to this which we can never allow ourselves to forget. It's easy to talk about 'we' and 'us' as though the fact that we belong to the same tribe as those who've suffered terrible losses, through bereavement or injury, gives us the same right to a voice as them. At one level, it does. Anyone travelling in central London on 7/7 could have suffered what those killed and injured on that day did. But that voice should be quieter, more reflective and less confident.

I believe that Christians have something unique to contribute to our national discourse about this. Our faith is rooted in the idea of grace, forgiveness and the universal fatherhood of God, who loves the murderer as he loves the victim. In the hate-filled world of the jihadis, that's a scandal. It subverts everything they want to do, transforming the vicious circle of atrocity and revenge into a virtuous circle of redemption and healing.

But it's also a scandal for those who have been deeply, deeply hurt by their actions, and continue to suffer the consequences today. These are people like former Bristol vicar Julie Nicolson, whose daughter Jenny died and whose faith was tested almost to destruction. She is someone with the rare gift of analysing and articulating the effects of grief. Most of the bereaved are anonymous, with emotions that are just as profound and life-changing, but don't make a story. Many others, who were caught up in the blast but walked away, suffered later – and continue to suffer – from post-traumatic stress. Their bodies have recovered, but their minds bear the scars.

How can we talk to such people about forgiveness? Quietly, reflectively and hesitantly.

The idea of forgiveness is so deep-rooted in Christian tradition that we don't always think about what it means. We think it has something to do with liking the other person, or being friends with them. We think, perhaps, that it means regarding them as though what has happened had never happened, like pressing a 'reset' button. We imagine that a single act of will can undo the past.

None of those things is true. Forgiveness is complex, spiritually, emotionally and intellectually. It isn't about undoing anything. But it is about refusing to allow the future to be controlled by the worst of the past. It's about a conscious commitment to be nourished by the best. The fear, the anger, the resentment and the desire for revenge don't necessarily go away, but they are overmastered by the sense of God's grace, his gifts and his peace.

Christians are called to be light in a dark world. If we're faithful to our calling, the terrorists will never win. Light always overcomes darkness.

Follow @RevMarkWoods on Twitter.