More than ever we are aware of being a tiny part of the infinite sweep of time when we move from one century and one millennium to another.
Here at Windsor the first fortifications were started by William the Conqueror in the earliest years of this millennium.
The castle we see today is the result of continual evolution and change over the last 1,000 years.
And as I look to the future I have no doubt at all that the one certainty is change - and the pace of that change will only seem to increase.
This is true for all of us - young and old.
At my mother's 99th birthday last August I was struck how the inevitability of change affects us all, and how different were my mother's early years compared with those of my grandchildren.
Birthdays, like Christmas, are a good time to get the family together, and last summer we had all the generations well represented.
My mother's birthday was also an opportunity to have a photograph taken of the four generations together.
As a family we cover quite a time-span. My mother can tell us about elderly relatives from her childhood whose memories went back into the middle of the 19th century.
For many of their generation the future is a source of excitement, hope and challenge.
Tonight I am giving a reception in Edinburgh for people under the age of 30 from all over Scotland. They have been invited because they have already achieved success or recognition in their lives. I am looking forward to hearing what they think about the future.
It is so encouraging talking to these young people. They are able to look forward to a future of opportunity and greater achievement.
For others however the future is a cause of understandable anxiety.
The sheer rate of change seems to be sweeping away so much that is familiar and comforting.
But I don't think that we should be over-anxious.
We can make sense of the future - if we understand the lessons of the past. Winston Churchill, my first prime minister, said that "the further backward you look, the further forward you can see".
And it was this importance of history which was much in my mind when I opened the new Scottish Parliament in July this year.
Devolution in Scotland and Wales, and more recently the very welcome progress in Northern Ireland, are responses to today's changed circumstances, but they need to be seen in their historical contexts.
The Scottish Parliament is new, but its many links with the past were expressed through symbols and ceremony.
Traditions are important all over the world. Last month on my visit to South Africa I went to a township school in Alexandra, outside Johannesburg, which has received financial aid from Britain.
Africa has a unique place in my affections; and there is always something so very special about the warmth and enthusiasm of the traditional African welcome.
There was the same exuberance and happiness as I and other Commonwealth leaders arrived in Durban for the Commonwealth Heads of Government Meeting.
Many of us at this conference highlighted how the varied strands of our shared history have been woven together so that we can more effectively address the challenges and opportunities ahead.
Our common past has played a crucial part in bringing so many peoples together into the modern Commonwealth.
Looking out here over the streets of Durban you quickly get a sense of how people from different cultures have come together.
And it's the energy and creativity of this which is so very exciting. That to me is what the Commonwealth is all about.
As with the process of devolution in the United Kingdom, the Commonwealth reminds us all of the importance of bringing the lessons of the past to bear on the aspirations for a better future.
Talking to prime ministers and presidents in Durban, the need was brought home to me for all us to draw from our history those constant and unchanging values which have stood the test of time and experience.
Fairness and compassion, justice and tolerance; these are the landmarks from the past which can guide us through the years ahead.
These timeless values tell us above all about the way we should relate to people rather than to things. Thinking of others, not just of ourselves.
Earlier this year in Manchester I visited some of the emergency services, whose responsibilities day in and day out are based on concern for others.
As always they are on duty over these Christmas and New Year holidays. Some of these firefighters had gone well beyond Manchester to give assistance to others. Earlier this year this group had been working in very difficult conditions amongst the refugees in the Balkans.
Up and down the country people like these are working tirelessly to help others. They remind us of the responsibility of each and every one of us to show concern for our neighbours and those less fortunate than ourselves.
I believe that this provides us with the direction and resolve required for the years ahead.
The future is not only about new gadgets, modern technology or the latest fashion, important as these may be.
Caring for others
At the centre of all our lives - today and tomorrow - must be the message of caring for others, the message at the heart of Christianity and all the great religions.
This message - "Love thy neighbour as thyself' - may be for Christians 2,000 years old. But it is as relevant today as it ever was.
I believe it gives us the guidance and the reassurance we need as we step over the threshold into the 21st century.
And I for one am looking forward to this new Millennium.
May I wish you all a Merry Christmas and, in this year of all years, a very Happy New Year.
Full transcript of HM. The Queen's 1999 Christmas Message