It's a happy or unhappy curiosity that the fifth anniversary of the invasion of Iraq falls in the middle of what Christians term Holy Week. What it does do is provide a distinctive frame for discourse about the war, given that the two most prominent allied leaders identified with the invasion, George W Bush and Tony Blair, saw themselves as being engaged on Christian business.

Holy Week, which began yesterday, is the most significant period in the Christian year. As part of the season of Lent - traditionally a time for reflection and penitence - it commemorates the last week in the earthly existence of Jesus of Nazareth. Any significant piece of action which purports to be Christian has to pass through the filter of this terrible and glorious week, which features passion, dirty politics, corruption, betrayal, judgment, blood and gore. More tea, vicar?

For obvious reasons, followers of a man who preached the loving of enemies and turning the other cheek have had difficulties with war. In the early Christian Church, believers were forbidden to serve in the armed forces. Especially when Christianity became the official religion of the empire and came under the protection of the state, the theological agenda shifted from pacifism to questions about the circumstances under which Christians might legitimately participate in war. The evolving "just war" theory - indeed it's still evolving - laid down a number of criteria, including the rules that such a war can be waged only as a last resort, that the war's weapons must discriminate between combatants and noncombatants, that its violence must be proportionate to the injury suffered, and that the attackers must have legitimate public authority for their action.

The slow-motion train wreck which goes by the name of Iraq failed every theological test.

Right from the start, the lies, the hubris and the ideological blindness - not to mention the entirely predictable spiralling recruitment of terrorists - were on public display. To understand what was going on, we could do worse than turn to the prescient words of one of the greatest theologians of the twentieth century, Reinhold Niebuhr. In his prophetic book, The Irony of American History, published in 1952, Dr Niebuhr predicted that the winner of the cold war would inevitably "face the imperial problem of using power in global terms, but from one particular centre of authority, so dominant and unchallenged that its world rule would almost certainly violate basic standards of justice". Niebuhr was afraid that if America became that dominant nation, it would not recognise its own injustices toward others.

Fast forward to March 2003. The righteous lecturing about the dangers of weapons of mass destruction, while armed with the biggest arsenal the world has ever seen, was further evidence of a lethal disconnection from Christian values. The strutting under a "Mission Accomplished" banner was as far from the Christ of Holy Week as could be imagined. George W Bush, who said that Jesus Christ was his "favourite philosopher", talked the language of Christ while acting like a blood-stained Caesar.

We know about the western military casualties, but the shameful refusal to count the Iraqi dead and maimed is a stain on the reputation of the "Christian" west, recalling Dylan's words: The names of the heroes, I was taught to memorise.

They had guns in their hands, And God on their side . . . For you don't count the dead, with God on our side.

Tony Blair was the Christian cheerleader Dubya wanted, but not the critical ally he badly needed. Their actions inflicted serious collateral damage on the Christianity they professed to represent. Instead of being charged with war crimes - surely Lothian and Borders police could spare a few bobbies from the Sheridan inquiry - Tony Blair gets paid half a million pounds a year as an adviser to US investment bank JP Morgan. Jesus wept.

Yesterday, many churches throughout the world celebrated Palm Sunday. On that first Palm Sunday, Jesus strode into Jerusalem and confronted its dirty money and its dirty politics. His subversive preaching and prophetic actions triggered an unholy alliance between "Church" and state which ended in the execution of the founder of Christianity as a public criminal. How ironic that he would eventually be co-opted as a sanitised, inoffensive chaplain of so-called Christendom by various murdering Herods and hand-washing Pilates. More waterboarding, vicar?

The Jewish theologian Abraham Joshua Heschel once said about the war in Vietnam: "How can I pray when I have on my conscience the awareness that I am co-responsible for the death of innocent people in Vietnam? In a free society, some are guilty, all are responsible."

Christian values? Time for a penitential walk through Holy Week to examine the real thing.