A violent attack on your city can be a disorienting thing, even if you're safe many miles away. Just ask residents of Paris, Brussels or Orlando. Indeed, ask those who experience this kind of thing much more regularly in Mosul, Aleppo or Yemen.

Things move quickly. 'There's been an incident in Westminster,' a friend said yesterday afternoon. Soon, my head buried in Twitter, my phone buzzed with texts from family, checking I was safe. I was five miles away and completely fine. But when four police cars came hurtling down the street I was walking on, the whole came a little closer.

It was at once incredibly close and incredibly distant. Friends began to mark themselves as safe on Facebook. Terror had again come to London, but I was experiencing it through my phone. As I got home, my laptop and TV helped to establish the facts we knew. Media at its best will answer the 'what' questions. But it can only begin to answer the 'why' questions.

The philosopher Jean Baudrillard wrote about the increasing sensation of experiencing events like these through contemporary media. In The Transparency Of Evil, he said, 'At home, surrounded by information, by screens, I am no longer anywhere, but rather everywhere in the world at once, in the midst of a universal banality – a banality that is the same in every country.' In other words, the media can help us to establish what has happened, but while our heads seek knowledge and facts, our hearts need something more.

At a time of violence, we seek reassurance, contact with loved ones – and something deeper. We seek communion.

This is unsurprising. As Christians, we believe humans are created for relationship. With anxiety heightened by a terrorist attack, we don't just want reassurance that those we love are safe. We need, viscerally, to actually be in relationship at that moment.

A phone call, a text message, a Skype chat, whatever it may be – we create a microcosm of our relationships in defiance of the prevailing circumstances.

Far more than sharing memes, this is how we resist terrorism. We do relationship. It may be with actual family that we live many miles from, it may be with friends near or far. For many of us, it will be with our church family. Countless London churches and those elsewhere opened up almost immediately for prayer and reflection.

In the theology of St Augustine, evil isn't a 'thing' at all. It has no attributes, cannot build anything and can only tear down the creative and positive work of God. It has no substance. The evil which was visited on Westminster yesterday couldn't create, but could only harm people, relationships and families.

Our response is what defines us. By gathering in communities of diverse and people and building, with the help of the spirit of God, a new family and community we are actively resisting evil.

This evening, I'll go to a service of communion where we will not only experience the presence of God, but we will also share the peace with each other. We will shake hands, maybe hug, real people in a specific time and place and look them in the eye while offering the peace of God to each other. This is more than just 'community cohesion'. Building a 'eucharistic community' is what challenges evil most of all. Eucharist, one of the words Christians have historically used for the Lord's Supper, the Mass, Communion, means 'thanksgiving'. We give thanks, in part, for each other.

Greg Boyd is a theologian whose thinking has been incredibly helpful in this area. His new book, The Crucifixion of the Warrior God, looks at the cosmic battle between good and evil.

In a previous work, God At War, Boyd has a passage which speaks into our predicament today. He says: 'We are not to accept with pious resignation the evil aspects of our world... Our revolt is to be broad – as broad as the evil we seek to confront, and as broad as the work of the cross we seek to proclaim. Wherever there is destruction, hated, apathy, injustice, pain or hopelessness... we are in word and deed to proclaim to the evil powers that be, "You are defeated." As Jesus did, we proclaim this by demonstrating it.'

That is what Christians across London will do today and in the days to come, and we invite everyone to join us.

Follow Andy Walton on Twitter @waltonandy