LONDON — The pope who already has made such a huge impact in America is, as even those most ignorant or hostile toward him must have noticed by now, a shy and scholarly octogenarian.

Though he speaks fluent and idiomatic English, the former Joseph Ratzinger has a strong German accent. So he does not fit any of the categories into which celebrities normally go. Worse still, he is inevitably compared to his heroic and highly charismatic predecessor, John Paul II, whose canonization is imminent. A saint is a hard act to follow.

Yet Benedict XVI has swept Americans off their feet, by the simple fact of his transparent, radiant integrity. Here is a figure who, more than any person now alive, represents the conscience of mankind. President Bush was right to greet Pope Benedict XVI as a foe of fanaticism, contrasting those who “evoke the name of God to justify acts of terror” with his “message that God is love.”

As Mr. Bush said, the pope is not afraid to denounce “the dictatorship of relativism,” to call evil by its name, and to make firm moral judgements. Whether or not you agree with particular judgements — on abortion or euthanasia, on stem cell research or Aids, on homosexuality or Iraq — is not the point. You may disagree with every one of the established doctrines of the Catholic Church — and yet be glad that a man like Benedict is pope.

For we live in an age of moral evasiveness, of equivocation, hypocrisy, and hype. Pope Benedict stands in uncompromising opposition to all that and much more. He faces up to accusations bravely. To the charge that the Church had shielded child abusers, he replied already on the airplane to journalists: “I am profoundly ashamed. Pedophiles will be completely excluded from the priesthood. It is more important to have good priests than many priests.” These are not the words of a man who is indifferent to the suffering of the victims. It was important that the pontiff should personally draw a line under what has been a long and traumatic ordeal for American Catholics.

But the pope has come to bring more than reconciliation. His two major encyclicals have been devoted to love and hope, and these are the blessings that he believes America needs most right now. Hope is the basis of action, and Benedict understands that only America has the energy, the motivation, and the ability to save Western civilization from its own moral turpitude.

Unless the West believes again in the Jewish and Christian values that underpin its culture and politics, the world is in for a 21st century that could even surpass the 20th century in horrors.

So the stakes are very high, and Benedict knows it. His speech at Regensburg in 2006 sent shock waves through the Muslim world: not just because the pope quoted a medieval Byzantine emperor insulting Mohammed, but because he put his finger on Islam’s most vulnerable point. If God is above reason, then men may invoke God to justify the irrational. And that is exactly what Islamist terrorists and the imams who brainwash them do.

Benedict showed how the Jews and Christians incorporated the rationalism of Greek thought into the heart of their faiths, but Islam turned its back on the legacy of the ancient world. From this divergence, much blood has flowed. If there is to be a lasting rapprochement between Islam and the West, it must be on the basis of reason and faith finding a new modus vivendi.

If the West is to survive, however, it must rediscover the spiritual sources of its own civilization. Benedict knows how hard it has become, in a culture where secularism is aggressively seeking to exclude religion from the public square, for the still small voice to be heard at all.

But he has a double answer to militant atheism: to reason with the open-minded and to fill the open-hearted with awe before the beauty of holiness. So he has reformed the liturgy and music of the Church, restoring Latin to a place of honor while also elevating the language of the vernacular Mass.

In his books, Benedict has given those who are curious about the Catholic faith the best introduction they can find. His life of “Jesus of Nazareth,” written while he was pope, became an instant classic not just by virtue of his authority, but by his appeal even to non-Catholics.

Benedict still has to fulfil the promise of his pontificate, and this visit to America is a crucial step toward doing so. Hitherto he has seemed a very Eurocentric pope, though he has good reasons for thinking that Europe is uniquely important and uniquely endangered.

Now he has reached out to what is still the world’s largest and wealthiest Catholic community — wealthy, that is, not only in financial but in intellectual resources.

America not only has more Catholic universities than the rest of the world, but it also has more impressive Catholic writers and thinkers. Figures such as Michael Novak, George Weigel, and Richard John Neuhaus have few, if any, equivalents in Europe.

Pope Benedict may not always agree with these American theologians, but he listens very carefully to everything they say. Nowhere else in the Catholic world is there such an influential body of opinion — the equivalent of the Franciscan and Dominican friars in the middle ages or, later, the Jesuits.

For all these reasons, and many more, Benedict XVI is happy to be in America. Past differences and suspicions are, temporarily at least, set aside.

This is a great pope and a good man, whose pilgrimage will end appropriately enough on Sunday at ground zero. New York will rightly give the pope a warm welcome. Here he is among friends — and not only Catholic ones.