The Queen's visit to the Republic is a hugely symbolic step in the long and troubled history of Anglo-Irish relations.
It signifies to the outside world that this island has achieved a political and constitutional equilibrium with its nearest neighbour.
Cooperation has replaced conflict. The new cordiality across the Irish Sea would have been nigh on impossible had it not been for the Good Friday Agreement and all that has followed since in the way of progress.
The visit could not be more timely because Northern Ireland is about to embark on a new style of governance. For the first time, we have the real prospect of a stable cross-community partnership between unionists and nationalists.
The constitutional issue has not gone away but it rests on a back-burner for the foreseeable future and our newly-elected leaders have a mandate to work together rather than apart.
This transformation in the political atmosphere lies at the heart of the Queen's visit to the south. Without what has happened here, she would not be in Dublin or Cork this week. The people of Northern Ireland, even more than the people of the Republic, have made her visit possible by pulling themselves out of the mire of physical force politics and voting for a new and broadly acceptable peaceful order.
No doubt this will be reflected in the formal addresses from the Queen and her host, Mrs Mary McAleese, for whom the visit of the British Monarch is the culmination of years of delicate diplomacy and the climax of her highly successful time in the President's residence in Phoenix Park.
However, the Queen's visit is far from risk-free. We must hope that it is carried through peacefully and respectfully because the international image of the Republic and of Northern Ireland is at stake. Much hinges on the historic events of the coming days.
None of us can be certain that the Queen's visit will not be disrupted by some dissident element. The shadow of the gunman and the bomber has not left these shores and, indeed, the high security activity and costs associated with the royal visit are evidence of the ongoing threat which still exists.
Old diehards may stick to their guns but even they must sense that the presence of the Queen on Irish soil is a sign of irreversible change. We are about to witness an exceptional turning- point in Anglo-Irish history whereby the ghosts of past conflicts can be exorcised.
When George V paid the last royal visit to the south exactly a century ago, the unionists of Ulster were starting to mobilise against Home Rule. Almost to the day, 95 years from the execution of the Easter Rising ring-leaders in May 1916, George's grand-daughter will be welcomed in Dublin and will lay a wreath at the Garden of Remembrance.
The Queen's visit has been a long time coming. I can recall writing the following in an Open Letter to her in this column nearly four years ago: "The longer you stay away the more your continued absence remains a sad reflection on the two societies on each side of the Irish Sea... I can think of no greater way to demonstrate a lasting Anglo-Irish peace than a warm and friendly handshake between a British Monarch and an Irish President on southern soil."
The Queen will be followed by the US President Barack Obama. The sympathy and economic support of the United States and Britain becomes all the more important in these trying times for the economy of the Republic and Northern Ireland.
We need all the help we can get. If the royal occasion is met with a real "Cead Mile Failte" welcome and displays a positive image of the Irish, so much the better for everyone.
Many who lived through the Troubles have bitter memories. Some can forgive, others simply cannot, but what we must not do, is allow the past to destroy the future for a new generation.
I suspect that is the message which our politicians were given on the doorsteps during the election campaign.
It is a pity that it has taken the British and Irish so long to get to this point and for the Queen to replicate what she has done in the way of visits to other countries, not least Germany, which were in conflict with the UK.
Life must move on. I hope it will on the streets of Dublin and Cork in the next few days.
The royal visit has potential to underpin the mood of change, north and south. When the Queen lays her wreath at the Garden of Remembrance and visits Croke Park, she will be drawing a line in the sands of time. Not before time.