Writing in the Mail on Sunday, Archbishop Justin Welby reflects on the challenges involved in reuniting the country after Brexit. 

The image will not go away. The tower, black and smoking, the odd glow of flame, a stream of water directed at it. Below, surrounded by London's bustling summer streets, I saw fire officers slumped in exhausted sleep, grimy in their yellow protective clothing. Air bottles from the breathing equipment lay heaped in piles, witness to dedication and barely imaginable courage.

We watched a drone whirr into the air to inspect the charred hulk for safety. Groups of those with the unspeakable duty of sifting through the ruined homes for bodies stood waiting and talking.

I was there with the Bishop of Kensington, Graham Tomlin. He had been on the scene for hours already and would stay for the next few days, alongside local clergy of all faiths. Plenty of the fire and police officers stopped to talk. Some asked for prayers.

Nearby, a local church was awash with noise and activity – Muslims, Christians and none-of-the-above all lending a hand. Diverse, buzzing, brilliant, this was London in active compassion.

Why am I starting with what I saw that day? Because Grenfell Tower and the terrorist attacks of the past few weeks comprise a storm of events that have tested our deepest values with an almost unrelenting ferocity – and brought out the best of communities in crisis.

The response to the Grenfell Tower tragedy from the emergency services and civic society – including churches and other faith groups – has been remarkable. It is matched by courage from those caught up in Manchester, Westminster, London Bridge.

Communities have staggered, stumbled and pulled themselves up. I am so proud and grateful to be part of a country where people at Westminster rush to treat a man who has just tried to kill them, where an imam ensures the would-be killer whose van is still resting on one of his congregation is protected.

I was moved to tears by those who risked their lives during the attacks; by the police, unarmed, sprinting towards the danger at London Bridge; by the Ariana Grande fundraising concert and the courage of Manchester.

However, the Grenfell Tower tragedy has also served to highlight divisions in our society. Many, including the Prime Minister herself, have recognised that support from the state has been inadequate in North Kensington. We have been severely tested in how we handle diversity, integration, social mobility and inequality. Failure in these areas is ultimately a failure of values.

In the terrorist attacks we have seen diversity integrated in community and decorated with courage. We know what we can be, both for good and ill, and we are at a moment where that difference sets our future. We have seen courage and generosity and all that makes for a good and flourishing society. 

We have also seen failures of government and a sort of tragic unwillingness to face the realities of divisions and people being left behind. We need to choose between the selflessness of the former and the inward looking 'me-first' attitudes of the latter.

Because this is, after all, a significant moment in our history, as the United Kingdom begins Brexit negotiations. For only the third time in two centuries, we find ourselves needing to redefine the place of our country in the world. Our approach to global issues will be defined by the values we practise here.

The subjects dominating the Brexit negotiations – trade, commerce, financial transactions – are important, but they are not enough on their own. Trading agreements are useless unless they serve individuals, communities and society.

Our values must be shaped by a recognition of the dignity of every human being, regardless of wealth, status or influence. They must be values lived at home so that when we play what I believe can and should be a leading role, it is a role for the good of the poorest of the world. People around the world will need to see that we are consistent, self-critical, showing in our own society the flourishing that we desire for every society.

Proverbs 29:18 says: 'Where there is no vision, the people perish.' But while high-flown words or soaring ambitions and vision may be an essential foundation, they must also be turned into policies, based in deep values of respect for all.

And policies must be joined to resources and actions so that they become realities. As we reimagine our future post-Brexit, not only do we need clear vision from politicians, we need delivery.

In numerous ways, we are already doing this – such as through spending a generous amount of national income on aid, our leadership in responding to ebola in West Africa and sending highly trained taskforces to places of vulnerability and conflict like South Sudan.

But recent events have highlighted the urgent need for a process of internal reconciliation, between regions, social groups, faiths and generations.

The future of this country is not a zero-sum, winner take all, calculation but must rest on the reconciled common good arrived at through good debate and disagreement.

Brexit continues to divide us. Exit negotiations will be fierce and the differences on what we should aim for, and how, are very deep. They divide our politicians and our society. With a hung Parliament, there is an understandable temptation for every difference to become a vote of confidence, a seeking of momentary advantage ahead of the next election.

For that to happen would be a disaster if our negotiators, faced with the united determination of the EU, go into the room without confidence in their backing in the UK. It might turn us inwards and forfeit the opportunity to be a country the world admires and blesses for our generosity and vision.

Politics is rightly hard and tough. We must not pretend otherwise. But for Brexit, we need the politicians to find a way of neutralising the temptation to take minor advantage domestically from these great events.

We must develop a forum or commission or some political tool which can hold the ring for the differences to be fought out, so that a commonly agreed negotiating aim is achieved. Obviously it would be under the authority of Parliament, especially the Commons. It would need to be cross-party and chaired by a senior politician, on Privy Council terms. It could not bind Parliament, but well-structured it could draw much of the poison from the debate.

A country united after Brexit is essential if we want a country that is resilient under the threats we face, capable of ensuring that the victims of Grenfell Tower are cared for and its lessons learned, and courageous in making our way in the post-Brexit world. The decisions we make over the next two years will have an impact for generations to come.

Let us do everything we can to ensure the right values are at their heart.