At 78, he is frail and bent. That rugged, athletic figure has been worn down by Parkinson's disease, by the assassin's bullet that tore through his intestines in 1981, and by two decades of ceaseless toil. He used to ski for hours; now he leans on his old ski-sticks for support while taking gentle walks. His voice used to be so powerful and clear, with a skilled actor's delivery that John Gielgud once described as "perfect". Now it is often slurred. His broad, smiling face used to radiate human warmth for a hundred yards around - a quality he shared with his "fellow Slav" Mikhail Gorbachev. Now the face is half-frozen with Parkinson's. His left hand trembles uncontrollably.
Yet still you glimpse flashes of the old magic, as the distant figure, all in white, draws a whole crowd to him with a characteristic gesture: gently but repeatedly lifting two outstretched open hands. Then he speaks to half a million people as if he were talking to one person. It's the old magic that I saw in communist Poland, where he dissolved the fear instilled by all Brezhnev's divisions with one wave of that now trembling hand. And still he goes on admonishing the rulers of this world, whatever their political colour, whether Castro or Clinton. Still he offers succour to the poor, the weak, the sick, the oppressed in every land.
You might think from this opening hymn of praise that I'm a Catholic, even a papal groupie. Far from it. Indeed, if I were a Catholic, I might be much less enthusiastic. His fiercest critics are among his own flock. I leave it to them to argue about his restoration of a "monarchical" papacy and the stifling of debate inside the church. As an agnostic liberal, albeit one rooted in a rich humus of Christianity, my concern is not with the church but with the world. And I want to argue that Pope John Paul II is simply the greatest world leader of our times.
I say this not just because of what I saw him do in Poland, although of course that counts. Nor is it simply because I have experienced the force of his personality in a small gathering, although that was unforgettable. Over these 20 years I have had the chance to talk with several credible candidates for the title of "great man" or "great woman" - Mikhail Gorbachev, Helmut Kohl, Vaclav Havel (who comes to Britain again next week), Lech Walesa, Margaret Thatcher - but none match Karol Wojtyla's unique combination of concentrated strength, intellectual consistency, human warmth and simple goodness.
Yet my case rests on his public record. No one has conveyed a better message, more effectively, to more people. What is this message? When he arrived on St Peter's throne, it was all there, fully formed, ready to go. He immediately wrote it down, in longhand, for his first encyclical, Redemptor Hominis ("The Saviour of Man"). But there's a problem here. A philosopher, poet and playwright as well as a pastor, he writes in a dense, difficult linguistic blend of Thomism (the philosophy based on the teachings of Thomas Aquinas), phenomenology and Polish Marian mysticism.
One common mistake is to suggest that he looks at the whole world through a Polish prism. Of course he is profoundly Polish. If you ever doubt that, just listen to him speaking directly to the Virgin Mary before the great monastery of Czestochowa, addressing her as "the Queen of Poland". (It's also deeply moving, for he really is like a man talking to his mother. His own mother died when he was eight.) But when I once had dinner with him, in a circle of Polish friends, speaking Polish, I was struck by the very opposite impression. Here was a man who looked even at Poland through the prism of his global experience, faith and mission.
The other common mistake is to interpret him in conventional political categories. Many in the West see him as just an old, dyed-in-the-wool reactionary. Gorbachev, by contrast, says the Pope is a man of the Left. In fact, he has always been fiercely critical of both capitalism and communism. But, as he insists in one of his encyclicals (Solicitudo Rei Socialis), the church's doctrine is "not a `third way' between liberal capitalism and Marxist collectivism". Tony Blair please note. Rather it is "a category of its own" - not ideology but theology. On the plane out to Poland for his first, great pilgrimage in 1979, he told journalists that the differences between communism and capitalism are superficial: "underneath is where the people are."
His first concern is with what he believes to be the presence of God and Christ in the world. But translated into the language of secular politics, his message becomes a set of demands to those who wield political, economic or cultural power, demands on behalf of the people "underneath". And a matching set of appeals to those individual people. At the centre is always what he calls "the human person" (comprising, in Catholic teaching, body, reason and soul). He insists that each and every individual human being has an ineradicable dignity and inalienable rights. John Paul II's passionate embrace of the language of human rights, previously associated with the heirs of the Enlightenment, was little short of revolutionary. He told Fidel Castro to respect his citizens' human rights, but also General Stroessner in Paraguay.
Everywhere, he takes the part of the poor. He may condemn "liberation theology", but his Latin American homilies have been full of the liberation theologians' concerns for the oppressed. His demands for "social justice" make pure, neo-liberal free-marketeers squirm. The right to work belongs to his core notion of human dignity.
Another great theme is tolerance and mutual respect between different peoples and faiths. He grew up with Jewish schoolfriends in pre-war Poland, and reconciliation between Christians and Jews is close to his heart. He has not gone as far as some Jewish leaders would like in acknowledging the Catholic church's historical responsibility for anti-semitism, but he has gone further than any of his predecessors. He also reaches out to Islam. Visiting Zagreb, he ordered Catholic Croats to respect the "outstanding presence" of Muslims in the Balkans.
Everywhere, too, he preaches peace. Even in Nazi-occupied Poland, he refused to support armed resistance. "Prayer is the only weapon that works," he told a friend. In Japan, he cried "Never again Hiroshima! Never again Auschwitz!" In Ireland, he told the IRA to abandon the violence that would "ruin the land you claim to love and the values you claim to cherish". In Britain, he criticised the Falklands War. And he opposed the Gulf War too. All peoples have a right to justice and sovereignty, he says, but these may only be achieved by non-violent means. As he told fellow Poles in 1983, when General Jaruzelski had tried to dash their hopes with tanks, "you must defeat evil with good".
Not only has he kept saying these things on 84 foreign trips, from Argentina to Yamoussouka. He has also dramatised them, with the skills of the professional actor he once nearly became. He has the ability to capture compassion in a photographic image: the gentle embrace of a crippled child, the head bowed in sadness at a place of horror. Yet he can also make the mighty tremble. Literally so in the case of General Jaruzelski, whose knees we could see shaking before he met John Paul II in 1983. "But only at the beginning," the Pope commented kindly.
Politically, his most obvious contribution was to the end of communism. Gorbachev himself says "everything that happened in Eastern Europe would have been impossible without the presence of the Pope". I would add "including Gorbachev". Without the Pope, no Solidarity in Poland. His great pilgrimage in 1979 broke the barrier of fear and created the solidarity that paved the way for Solidarity. This was far more important than anything in his biographer Carl Bernstein's over-excited tale of a "secret alliance" between the Vatican and the CIA.
Also, without Solidarity, no Gorbachev. I don't mean, of course, that Gorbachev would not have emerged as Soviet leader. I mean that he would not have made his seminal revision of Soviet policy towards Eastern Europe unless the persistence of Solidarity - despite Jaruzelski's tanks - had shown him that the Soviet Union just could not carry on in the old way. And when Gorbachev gave an inch, the Poles took a mile. Here is the specific chain of causation that goes from the election of the Polish Pope in 1978 to the end of Communism, and hence of the Cold War, in 1989.
If this was his clearest positive contribution to world history, then his largest negative contribution has been his opposition to all forms of artificial contraception. Here, too, he has been nothing if not consistent. He came to this position after thinking deeply about love, marriage and sexuality as a young priest. He personally encouraged Paul VI to take his stand against the Pill in the fateful 1968 encyclical On Human Life (Humanae Vitae). He once said to a friend who challenged him on the subject: "I can't change what I've been teaching all my life." But the result has been much needless, avoidable suffering, as women in the third world, denied contraceptives or proper education on birth control, have brought unwanted children into lives of misery. Yes, that very poverty and misery against which his own heart cries out.
After seeing off Communism in the Eighties, he has spent the Nineties attacking the evils of unbridled capitalism. He tells us, far more robustly than any of the parties "of the Left" which again rule in Europe, that the rich still exploit the poor and the North damages the South. He says we are caught up in the pursuit of "having" at the expense of "being". He says consumerism is "a web of false and superficial gratifications". Turning red in the face with anger, he rails against liberty decayed into license, sexual promiscuity, alcoholism, drugs, relativism and post-modernism. Most people, even in his native Poland, ignore the old man's warnings. But are we really so sure there is no truth in what he says about our own world, a world more free than it has ever been before?
As I write, I have before me a little book, some five inches by three. A miniature anthology of the Pope's teaching, it's called Agenda for the Third Millennium. Who else would dare such a title? I can't get anywhere with half of it, because I, like most of humankind, no longer believe. But there are things in the other half that I find magnificent, rich and true. And important, too, for the next 20 years - never mind the next thousand. It may not be the agenda for our time. But do any of us have a better one?
Timothy Garton Ash's `The Polish Revolution: Solidarity' will be reissued by Penguin Books next spring, when his new book on Europe in the Nineties will also be published.