The world lived this death. It was a global Calvary. People from every corner of the earth gathered in St Peter's Square, peering up at those two windows of the papal apartment, illuminated against the night sky. Across five continents, Christians, Jews and Muslims joined them through television. Marcello, from Rio de Janeiro, emailed CNN: "We are watching the agony of the greatest man of our time." Mohamed, from Birmingham, emailed the BBC: "He will be missed by Catholics and non-Catholics alike."
What does this tell us? It tells us that Pope John Paul II was the first world leader. We talk of Bush, Blair or Hu Jintao as "world leaders", but they are merely national leaders who have a world impact. That's true even of Nelson Mandela, his closest contender for Marcello's title of "greatest man of our time".
Pope John Paul II uniquely combined three elements. He was the head of the world's largest supranational organisation of individual human beings. (The UN is an organisation of states; the Islamic umma is not an organisation.) He believed withunshakeable conviction that his message was universal, applying equally to every man, woman and child - Catholics and non-Catholics alike. And he seized the technological opportunity of bringing that message personally to almost every country on earth, thanks to jet aeroplanes and television. In short, he made the world his parish. No one had ever done this before. No one could.
As an agnostic liberal, I don't feel qualified to judge what he meant for the Catholic church. But I think I can judge what he meant for the world. John Paul II was, quite simply, the greatest political actor of the last quarter-century. I use the word "actor" in a double sense. Theatre was the second passion of the young Karol Wojtyla, even in Nazi-occupied Poland, and he was a talented stage performer. Before the onset of Parkinson's disease, he had a lovely voice. The actor John Gielgud described his delivery as "perfect". He had this extraordinary ability to speak to a crowd of a million people so that each and every one felt he was talking to them individually. He spoke in images as well as words (look at that photo of him in a sombrero carrying a Mexican child) and his personal warmth came across on television.
We also use the words "political actor" to mean a person who makes things happen in the world, as in the portentous American phase "a global player". I watched at close quarters John Paul II's impact on the Soviet bloc, from his election in 1978 to the collapse of the Soviet Union in 1991. No one can prove conclusively that he was a primary cause of the end of communism. However, the major figures on all sides - not just Lech Walesa, the Polish Solidarity leader, but also Solidarity's arch-opponent, General Wojciech Jaruzelski; not just the former American president George Bush Senior but also the former Soviet president Mikhail Gorbachev - now agree that he was. I would argue the historical case in three steps: without the Polish Pope, no Solidarity revolution in Poland in 1980; without Solidarity, no dramatic change in Soviet policy towards eastern Europe under Gorbachev; without that change, no velvet revolutions in 1989.
Karol Wojtyla's political vision included the reunification of Europe. So long as he still had breath enough to speak, he talked of eastern and western Europe as the continent's two lungs. He lived to see this vision realised, as eight central and east European states, including his beloved Poland, joined the European Union last May.
Yet his largest legacy may lie not in the first world (of democratic capitalism), which he inhabited and enlarged, or the second world (of communism), which he destroyed, but in what we used to call the third world. John Paul II was a consistent spokesman for the half of humankind who live on less than $2 a day. This is also the part of the world where most Catholics are now to be found. He preached, tirelessly, every person's right to a minimum of human dignity. "I speak," he said, "in the name of those who have no voice." It was not just in communist-ruled eastern Europe that he spoke up for freedom. Opening an old file of newspaper cuttings, the first one I find is headlined "Pope takes issue with Stroessner on freedom". It records him reading the Paraguayan military dictator a fierce lesson about the importance of human rights and of free speech.
The familiar claim that he was "socially conservative" is a gross oversimplification. He consistently admonished third world dictators and western capitalists about the need for social justice. In a small Polish-speaking group I once heard him say, very plainly, that he deplored unbridled capitalism as much as communism. He was also utterly consistent in his advocacy of peace, from criticising the impending Falklands war when he came to Britain in 1982 to opposing the Iraq war in 2003. In Japan, he cried: "Never again Hiroshima! Never again Auschwitz!"
One of his policies did great damage in the developing world. Maintaining and reinforcing Pope Paul VI's ban on artificial means of contraception, he caused unwanted children to be born into poverty and, increasingly, with HIV/Aids. Challenged by a friend, he said: "I can't change what I've been teaching all my life." We must hope that his successor will reverse this policy.
Some say he was lost in the post-9/11 world. Actually, no one has done more to avert a "clash of civilisations". He reached out to Jews and Muslims, as well as to Christians of other churches, in a way no pope had ever done before. And the message got through - witness that email from Mohamed in Birmingham.
"What will survive of us is love," wrote the poet Philip Larkin. John Paul II will survive in the memories of millions who loved him. But even for those who did not love him, including many western secular liberals, protestants and liberal Catholics, the legacy of this first world leader is a challenge.
At the beginning of the third millennium, we have economic globalisation. We have the globalisation of information, represented by the internet and CNN. We should have international institutions and laws to match. But that in turn requires what has been called moral globalisation. Whether or not we share John Paul II's motivating beliefs, we can acknowledge that his was the most impressive attempt so far made by any single human being to spell out what moral globalisation might mean, starting with a lived practice of universal sympathy. After he preached at Auschwitz in 1979, a nun, kneeling before him, whispered: "I am a Polish nun. But I am also a Russian Jew." In 2005, we need to say: "I am a prosperous westerner. But I am also a woman of Darfur." And then to act accordingly.
Now we must do this on our own.
· Timothy Garton Ash is the author of The Polish Revolution: Solidarity and, most recently, Free World