I've waited a while before my final response - and the end of this dialogue - because this debate is about as important a one as we can have in any time, and yet it seems particularly urgent at this time. The reason I have found our dialogue helpful is because we actually agree on some core issues. Maybe it's worth pointing them out. We both accept the role of some mystery in the universe, something we cannot yet explain, something humans may never be able to explain rationally. You air this at the end of your book, "The End Of Faith," where you describe your own Buddhist experimenting and meditation. We also both accept the danger of fundamentalism. In many ways, both our books are aimed at fundamentalist politics, and the existential peril it threatens in an age when the technological capacity for mass destruction is world-threatening.

We disagree on how best to understand mystery and how best to counter fundamentalism. You write:

You want to have things both ways: your faith is reasonable but not in the least bound by reason; it is a matter of utter certainty, yet leavened by humility and doubt; you are still searching for the truth, but your belief in God is immune to any conceivable challenge from the world of evidence. I trust you will ascribe these antinomies to the paradox of faith; but, to my eye, they remain mere contradictions, dressed up in velvet.

I hope this dialogue has shown that I am indeed bound by reason - up to the point where reason tells us little or nothing at all. We may disagree where that boundary is. There is more space beyond my reasonable barrier than yours, more content, more meaning. But since I do not claim that my faith must in any way impinge on your life or on anyone else's, I fail to see how my Christianity is less reasonable than your different, and more modest embrace of mystery. Or less reasonable than Einstein's dictum, relayed in Walter Isaacson's new biography:

"Try and penetrate with our limited means the secrets of nature and you will find that, behind all the discernible laws and connections, there remains something subtle, intangible and inexplicable. Veneration for this force beyond anything that we can comprehend is my religion. To that extent I am, in fact, religious."

I am more religious than Einstein, because I have experienced the love of Jesus and his redemptive, transformative power. But I fully concede that this is a gift, not a theorem. I hope it's clear I think no less of you for not seeing it or for seeing only so far as Einstein; and when I see this gift more fully realized in others - like the monks in the Grande Chartreuse - my response is not to feel frustrated by them or fearful of them, but simply to watch and listen to what they have to say in their silence. As long as they leave me alone - and all genuine Christians leave others alone - I am in awe of them.

But I agree that we are in a civilizational crisis outside the monastery's walls. Fundamentalist religion is on the march, its certainty dangerous, its ambitions terrifying, its capacity for destruction incalculable. In my more realistic moments, I have come to accept the inevitability of large-scale global destruction in my lifetime. The odds against it aren't great. Islamist countries already have nukes; a particularly extreme faction in Iran may soon have access to them; Islamists are not only capable of inflicting Armageddon, they clearly want to. They are not subject to intimidation, which is what makes religious faith at its most intense so powerful. They cannot even be stopped by force. We have learned that in Iraq. Bullets cannot change hearts. It is so easy to destroy; it is so hard to build.

Your answer to this crisis is an attempt to abolish the legitimacy of all faith-based discourse, to end the toleration for religiously-rooted argument, to "end faith." I respect your intentions here, even though I do not share them. But I do not see that this can ultimately solve our problem. In fact, by attacking and undermining those of us who sustain a non-fundamentalist faith, you may make the problem worse. The irredentist and fundamentalist remnants, freed from any internal religious discourse with the rest of us,  and cordoned off from respectable discourse, may well become even more extreme.

Convinced that the choice is solely between fundamentalism and atheism, the vast majority of believers will then be trapped perforce in the fundamentalist camp. Given the ubiquity of faith, given the absence of any civilization in human history that has been free of it, given the evolutionary and biological inclination toward faith, given the respect that a man even as rational as Einstein paid to the "veneration" of the force beyond all of us, your project is absurdly utopian. And like many utopians, you may, I fear, be making hell on earth more likely.

I say this not as a form of prescience but as a matter of hindsight. Although no genuine human civilization has been built on non-faith, in the last couple of centuries, several experiments in atheist and rationalist government were indeed carried out. You may recall the guillotine - synonymous with the dawn of the rational Enlightenment. Religion was also extirpated by force in the Soviet Union and Communist China; it was coopted by the state in Nazi Germany; in Pol Pot's Cambodia, the record of atheism in contrast with religion is quite clear. Atheism will never occur spontaneously among humans in large numbers. But when it has been imposed by force, it has been one of the most violent, evil and destructive forces in human history. Religion has a bloody past that I do not begin to deny. Fundamentalist atheism's is bloodier.

The relevant categories are therefore not, I would submit, faith and reason. The categories are those who rely on reason alone, those who use faith to trump reason in all respects, and those who understand that human life is inherently a balance between the two. Your faith-free world is not a human one; and it is not in that sense a rational one. My response is a balance, a triangulation of sorts. And a triangulation is not a contradiction.

In trying to address the global crisis we agree upon, I have two responses. The first is classical liberalism, as expressed in the American constitution, and constructed by Hobbes, Locke and their Enlightenment successors. That is my first political response, and it is central to my book on political conservatism. (My Oakeshottian politics amounts to a contingent and conservative defense of Anglo-American liberal constitutionalism.)

But the second and deeper response is Christianity itself, at the core of which is a radical refusal to force anyone to do anything. That is what the cross means to me: voluntary submission to violence as the only way to transcend violence; submission to death as the sole means to overcome death. A regular reader makes the point as well as I can:

"Humanity will not survive unless it grows beyond war. Period. We are too powerful. We have to grow up. Jesus was not speaking to his generation. He was speaking to the future. He was speaking to us, and to our children. Note that he did not say "damned are the war-mongers". He said "blessed are the peace-makers." His accent was on the positive, the creative, the way forward, the way out. Think about that phrase, "make" peace. Peace is not the absence of war. It is not a vacuum. It is a thing, a positive quality, in fact the divine quality. It must be created, in our hearts and in our minds, and in our world. Peace must be made, like you make a house, a cake, a painting, a book. That's the whole point of human life, to embody the divine in whose image we are made.

Irony of irony, this is also the real meaning of jihad. We are not fighting the Islamists, and they are not fighting us. We are all fighting ourselves. Until we see that, until we rise above, we will stay caught in the vicious circle of projection and violence and projection. Jesus showed us the way out: become a peace-maker. That does not preclude self-defense. But it goes far, far beyond self-defense."

I am not a pacifist. I believe in just wars when necessary and a strong defense to deter mischief. I supported Clinton's war in the Balkans and Bush's war in Afghanistan and, at first, in Iraq. But I am not unchastened by Iraq - and what it has told us about the struggle we are in. I wonder if the Christian calling now is therefore what it has always been, but more urgent than ever. This earth we inhabit is in peril, and our generation's task is to protect it. I don't mean merely the environment, although its sickness is clearly a function of our spiritual decay, our preference for material gain over spiritual calm. I mean the real and terrible danger of terroristic warfare, the kind that is now ravaging Iraq and raped New York City nearly six years ago. Instinctively, I am a realist. I know the odds of surviving this with our civilization intact are low. But I also think I know the only fundamental long-term answer. It is non-violence as Jesus practiced it, love as Jesus taught it, hope as Jesus promised. This requires work - and paradoxical work - to accept our gangsterish nature, to acknowledge abuse of faith in fundamentalist certainty, to stay realist about how to keep the peace and defeat real enemies - and yet also to practice the faith that alone can save our world.

Thomas Merton wrote:

"Faith of course tells us that we live in a time of eschatological struggle, facing a fierce combat which marshals all the forces of evil and darkness against the still invisible truth, yet this combat is already decided by the victory of Christ over death and over sin. The Christian can renounce the protection of violence and risk being humble, therefore vulnerable, not because she trusts in the supposed efficacy of a gentle and persuasive tactic that will disarm hatred and tame cruelty, but because she believes that the hidden power of the Gospel is demanding to be manifested in and through her own poor person. Hence in perfect obedience to the Gospel, she effaces herself and her own interests and even risks her life in order to testify not simply to "the truth" in a sweeping idealistic and purely platonic sense, but to the truth that is incarnate in a concrete human situation, involving living persons whose rights are denied or whose lives are threatened."

That self-giving, that risk of peace, that work of conciliation is the calling of our time. You hear it; and your work is an honest attempt to right what is wrong. But I do not believe that we can think ourselves into peace by reason; we can only work every day toward achieving it through love. That is what Jesus taught us before he taught us anything else. Be not afraid. Love one another. Peace be with you.

You may wonder why my faith endures. My answer is: because it is true and because, now especially, it must.