There is an electrifying moment right at the end of Stephen Rea's fiercely relevant production of The Plough and the Stars, which opened at the Gaiety Theatre in Dublin on Monday. The British tommies have just come on stage in the final scene. Bessie Burgess has been shot dead while helping Nora, mistaken for a rebel sniper who is active in the area.
The television is on, showing scenes of burning buildings. An English voice comes over the walkie-talkie. "Shoot the sniper. Shoot him dead." It is an uncanny echo of the tape, made by a local radio enthusiast, which was played to the Bloody Sunday Tribunal in Derry just a few weeks ago. It recorded a British officer ordering a soldier to shoot and kill a nail-bomber.
Stephen Rea has been criticised for taking liberties with O'Casey's great anti-war play, not least for updating it. For this reporter, watching it as we savoured a moment of hope in the peace process, it was almost unbearably moving. The characters on the stage, much younger than is usual in productions of O'Casey, could have walked off the streets of Derry or Belfast.
It also provided a salutary reminder that there is still a long way to go before we lay to rest the divisions and grief of the past. The innocent suffer, but for those involved this is a deadly argument between two irreconcilable views of nationhood. Securing a lasting peace means creating a space which can accommodate both.
In this context, last week's leak of a British government document which described Brian Cowen as "tacking to the green on every available occasion" is instructive. The memo, written by an unnamed British official, reports on a meeting between Peter Mandelson and the Minister for Foreign Affairs.
In the course of it Mr Cowen put forward the view that "beyond the constitutional acceptance that Northern Ireland remains part of the United Kingdom, there should be no further evidence of Britishness in the governance of Northern Ireland."
One is tempted to echo Chris Patten's question, posed in a different context, "What on earth did he expect?" This, in essence, is the compromise that lies at the heart of the Belfast Agreement. Irish nationalism accepts there will be no change in the constitutional position of Northern Ireland until a majority favours it.
In exchange, the British government pledges there will be equality and parity of esteem for both communities. If British officials are still experiencing difficulty grasping this concept, two years after the signing of the Belfast Agreement, there must have been something badly skewed in the dialogue between the governments.
It's a harsh truth, and one which is often unpalatable to people of goodwill, that this process works best when each government has a clear view of its own constituency. Put crudely, that means Dublin's primary responsibility is to represent the interests of Northern nationalists, while London safeguards those of the unionists.
That is what Peter Mandelson was doing when he suspended the Executive to save David Trimble, despite the objections of both the Irish Government and the republican movement. By doing so, he secured the confidence of many unionists and has thus made it easier, hopefully, for David Trimble to move forward.
Brian Cowen has played a similar role on the other side. Mr Mandelson may feel the Minister for Foreign Affairs "has no feeling for, or understanding of, unionist concerns". Against that, he has proved himself to be a tough-minded negotiator who tells it as he sees it to all sides. This has steadied the republican movement .
In the past it sometimes seemed Irish ministers, including the Taoiseach, were all over the place on decommissioning. That has changed since Brian Cowen arrived at Iveagh House. Sinn Fein trusts him. This has been a major factor in enabling the IRA to issue its statement pledging to put its arms "verifiably beyond use", a step which even many unionists recognise as historic.
Brian Cowen and Peter Mandelson may not be soulmates. Frankly, it is difficult to imagine either choosing to spend bonding time in the other's company. That does not matter, least of all to the many people in Northern Ireland who will live a better life if the Belfast Agreement puts down strong and lasting roots.
There are still obstacles to be overcome. In recent days it has become clear that policing could all too easily replace decommissioning as the issue most likely to scupper the present mood of optimism. John Taylor, who has welcomed the IRA's statement on arms, has also warned the whole deal could "unscramble" over the future of the RUC.
The issue is one which goes beyond names and symbols to the core issue of achieving consensus in Northern Ireland. Chris Patten put it well in the opening section of his report when he described the RUC as being seen by one community as "the custodians of nationhood" and by the other as "the symbols of oppression".
All the parties who signed up to the Belfast Agreement recognised the need for "a new beginning to policing in Northern Ireland with a police service capable of attracting and sustaining support from the community as a whole". Most unionists, including many serving RUC officers, know this must happen. The challenge is how to do this in a way which reassures nationalists that fundamental change is on the cards while soothing the wounded pride of the unionist community.
Sometimes the most important moment in any negotiating process is when one side recognises the other needs a helping hand. If David Trimble wins the support of his party's governing body for the restoration of the political institutions, the situation in Northern Ireland will be transformed. Perhaps it is time for Brian Cowen, having persuaded the IRA to move forward, to throw a lifeline to David Trimble.