What unites the British Prime Minister, Tony Blair, the US president, George Bush, and the men who shouted "Allah akhbar" as they flew aeroplanes into the World Trade Center? They all have an inner certainty that comes from their religious beliefs. They believe that their God will guide them, so mere earthly disapproval is unimportant.
That is why, when discussing Iraq, Bush and Blair once knelt down together and prayed. That is why, as Bush said of Blair, "he doesn't need a poll or a focus group to know right from wrong". That is how they feel able even to defy their own religious leaders. Islamic terrorists are condemned by the leaders of Islam; and Blair - whom David Hencke and I, in our biography of him, "outed" as a closet Roman Catholic - was left in no doubt, when he visited the Pope last year, that the leader of his Church was opposed to the invasion of Iraq. They believe, as the Christian saints and martyrs used to say, that God will be their judge.
And that is why religion, and religious teaching, should be kept as far away from democratic politics as possible. There is no reason why democratic leaders should not have their own, private religious faith, so long as they understand that, for what they do in our name, they are responsible to us, not to their God.
The British, unlike the Americans, are instinctively distrustful of a politician who wears his God on his sleeve, which is why Alastair Campbell persuaded Blair to remove the words "God bless you" from one of his televised speeches on Iraq. But what they have is a prime minister to whom religious ideas are far more important than political ones. That is the key to his politics.
It is from his religion that Blair found the strength to take us to war in Iraq. Other prime ministers who have led us into war - Neville Chamberlain and the Second World War; Clement Attlee and Korea; Anthony Eden and Suez; Margaret Thatcher and the Falklands; John Major and Iraq - at least knew that their own party and friends agreed that war was necessary. Blair led us to war even though most of his cabinet started out opposing it, nearly all of his party were against it and those closest to him were privately queasy about it.
So the consequences belong squarely with Blair, right down to the dreadful death suffered by Ken Bigley, who was taken hostage in Iraq. That knowledge would crush most people, even most politicians. But it does not crush Blair. That is the measure of the man's certainty and self-belief, which is denied to leaders with no God to turn to.
God gives a leader strength, but it is the strength of a medieval autocrat, not of a democratic politician. According to the doctrine of the divine right of kings, the monarch derived his authority from his God, not his people. When James I remarked "No bishops, no king", he was stating the political reality that if he allowed the authority of the Church's leaders to decay, the king's authority would rot alongside it.
That's why we need constant vigilance to ensure that religious training gets nowhere near our politics courses. If we let our future political leaders, political commentators and politically aware people become tainted with the divisive certainties of theology, we will lose the fragile hold we have on them. We will also be helping to entrench the world's sectarian divisions. The last thing the world needs right now is political leaders who identify with one or other of the three great religious forces - Christianity, Islam and Judaism - and believe that theirs is the one true faith.
Theology will not train leaders to act in an ethical manner, only a sectarian one. The fact that a leader is a deeply religious person is not, and never has been, a guarantee that he will behave morally.
Let them learn political philosophy. Let them study Plato, Machiavelli, Adam Smith, John Stuart Mill and even the great religious political philosophers. Let them study competing ethical systems. Let them study philosophy; but for God's sake, keep them away from theology.
The Blairs and their Court by Francis Beckett and David Hencke is out now from Aurum Press