It tells us much about who we are as a nation and our enduring affection for tradition that millions will be glued to the television coverage of the ceremony at Windsor, and the good wishes of all of them go to the bride and groom.
Yet the ceremony also tells us that we are comfortable with how those traditions have gradually adapted themselves to an evolving, modern Britain which is at ease with diversity and inclusiveness, and that is further cause to celebrate today.
Only a few years ago, it would have seemed unthinkable that an American of mixed race who also happens to be a divorcee, as Meghan is, should marry into the Royal family.
Not any more. Now, the only reaction to her background or marital history is a resounding “So what?” How healthy that is, and what a cause for rejoicing that stuffy, irrational prejudices have been blown away.
That’s another reason for people to wave the Union Jack in celebration, as a symbol not just of national pride, but as an emblem of welcome, openness and goodwill.
Even by the standards of Royal weddings, today is a notable occasion. It is not loaded with constitutional significance, as the marriage of Prince William and Catherine Middleton was in 2011, because that was the wedding day of the man born to be King and the woman who would be mother of a future sovereign.
But Harry and Meghan’s wedding is, in a different and important way, just as significant because it reflects the society over which William will one day reign.
The couple are emblematic of the sweeping away of barriers of race and class to happy and fulfilling relationships. Their backgrounds could hardly be more different – Harry from the most privileged imaginable, Meghan from suburban US ordinariness.
The diversity of their origins and experiences reflect life – and love – in modern Britain. All over the country today, other couples from widely differing social and ethnic backgrounds will marry too. Their ceremonies will be rather less exalted than at St George’s Chapel, but no less joyous for all that.
And in mirroring the country as it is now, Harry and Meghan are heirs to a grand tradition that has served the monarchy well.
The Royal family is at its best, and most potent as the ultimate symbol of reassuring stability, when it is closely in tune with the mood of the people.
That applied during the Second World War when George VI was emblematic of Britain’s resolve, and it still applies today, whether at times of national joy or grief, when words from the Queen capture how the country is feeling.
The public affection displayed towards Harry and Meghan since their engagement was announced is rooted in the recognition that they are very much a couple of their times.
So it is too with William and Kate, and so it was 70 years ago when the young Princess Elizabeth and Philip Mountbatten were newlyweds symbolic of a country determined to forge ahead into a bright new age.
Today’s newlyweds will have a key role to play in safeguarding and developing the bond with Britain’s people in the years ahead, because William’s approach to Royal duties is a collaborative one in which he sees his younger brother as a vital component.
The closeness between William and Harry has long been apparent, and their reliance upon each other certainly grew more profound because of the tragic and untimely death of their mother, Diana, Princess of Wales.
Their joint campaigning for better help for young people with mental health problems has been given authority by their willingness to talk about struggling to cope with such a terrible bereavement as children.
This has placed Harry at the forefront of Royal life. And it will place Meghan there too, alongside Kate, as the two couples become joint faces of forward-looking royalty.
Though this might seem a different way of doing things for the Royal family, it really is only an updating of tried-and-tested tradition that has served the institution well throughout the Queen’s reign.
The Duke of Edinburgh’s definition of the family as “The Firm”, an entity that reflects the life of the nation and is seen to be working for the good of the people fits this dynamic new combination perfectly.
Brothers, sisters-in-law, parents, aunts, uncles – a firm of four people that for all its privileges and duties fundamentally looks very like countless other families in Britain, of whatever background, race or religion, and is in tune with them.
How shrewdly Harry and Meghan appreciate the need to do that has been demonstrated by the air of informality surrounding their wedding.
Ordinary people have been invited to Windsor to participate, but the political establishment will be absent. For all its trappings, this is a wedding that is less a state occasion than a family one that reaches out towards the wider community.
Even so, the Royal wedding will be everything the nation wants it to be – regal, dazzling, glamorous and a reason to feel good about our country.
But it will be something more, something that matters greatly in the long run, after the bunting and the Union Jacks are packed away until the next great Royal occasion.
Today sees Royal tradition updating itself as we watch. Rather like a long-married couple renewing their vows, the ceremony is a reminder that however much the relationship between royalty and people evolves, the bond between the two remains strong, and they have much to look forward to together.
Andrew Vine writes in The Yorkshire Post every Tuesday.