By Robert Pigott
Religious affairs correspondent, BBC News
Christianity's leaders are more easily identified
A total of 138 of the world's top Muslim leaders, clerics and academics have written an open letter to the Pope, the Archbishop of Canterbury and other leaders of the Christian world.
It warns that world peace depends on better dialogue between them, and points to the fundamental beliefs each have in common.
But the real significance of the initiative lies in the creation of a powerful new lobby in world politics.
It is certainly not the first time that Christian and Muslim leaders have referred to their shared values and traditions.
In the years of tension since 9/11 it has been a frequent accompaniment to inter-faith meetings and projects aimed to mend the fractured and suspicious relationship between some Muslims and Christians.
But the letter, written by ayatollahs, muftis, sheikhs, sultans, professors and ministers, has taken this assertion of cousinly - even brotherly - relations to another level.
That is partly because the signatories have a considerable personal influence, in countries as diverse as Russia, Egypt, Nigeria, Saudi Arabia, Malaysia and Yemen.
"Looking down the list of signatories, there is one person after another with large followings, often numbered in millions," said David Ford, professor of divinity at Cambridge University.
"The fact that they've signed it means it will be taken seriously at the grass roots."
Just what are the revelations that this impressive cast-list has signed up to?
The letter contains a clearly written account of the passages in the Koran and the Bible that illustrate close similarities in the most fundamental doctrine of Christianity and Islam.
For example each of them insists that followers worship only one God, and requires them to love their neighbours as themselves. Other passages strike a note of conciliation, even humility.
For example, there is the Koran's acknowledgement that the truths revealed to the Prophet Muhammad - the founder of Islam - had already been shown to the prophets of the Old Testament (the Jewish Torah) and the New Testament, including, of course, Jesus himself.
The document also picks out the verses in the Koran which tell Muslims that they should treat the followers of these Jewish and Christian prophets with particular friendship and respect.
It also cites the Koran's specific instruction that these "people of the Scripture" worship the same God as Muslims.
But the real significance of this gesture, is that it is the first act of a group that intends to become the "international voice" of mainstream Islam, missing for so long.
It has been one of the problems of dialogue between Christians and Muslims that Islam has lacked a coherent mainstream view.
It has little of the hierarchies that characterise Churches, headed by leaders who can credibly represent the faith.
Not only is there no Muslim pope, but there is barely a single voice, or even group of voices, generally acknowledged to speak for "global Islam".
It has produced a vacuum into which it has been easy for extremists to move, whether locally in a town or city, in a country or in whole regions.
Extremists, from maverick imams to the leaders of al-Qaeda, have found it easy to claim to speak for Islam.
"So often the extremists have been able to use the modern media," says Professor Ford.
"Now finally there is a platform, a mode, for the moderate, mainstream, traditional Muslim leaders to come together and find consensus."
Moderate Muslims have often been criticised for what is perceived to be their failure to speak out on more difficult issues than the shared basics of faith.
Michael Nazir-Ali questions the basis for dialogue
As well as Muslim terrorism, they include the lack of democracy in Muslim countries and the often violent treatment of Christian minorities, especially converts to Christianity.
One of the authors of the letter, Professor Aref Ali Nayed, says: "We can't solve all of Islam's problems with a single document."
However he agrees that what the 138 have begun with their statement is a powerful new voice in world politics in the making.
"Now we have the mechanism of getting all these scholars together to speak with one voice really worked out, we shall build upon it," says Professor Nayed.
"You shall see more scholars and more documents, and we shall address other issues, issues that are more difficult. But we must have the courage to face them."
By going back to fundamentals - the authors hope to undermine the fundamentalists themselves.
Reiterating the shared view of a single God and the command to "love thy neighbour", the letter strips away the baggage of history and culture and produces a blank sheet for a new relationship.
In a sense there is a greater potential for agreement across the religious divide than there is for healing the fractures within each religion, because no-one is asking or expecting the other for concessions.
However some have questioned the letter as the basis of dialogue.
The Bishop of Rochester, Michael Nazir-Ali, himself born into a Muslim family, pointed out that Christians' view of God - containing Jesus in a divine trinity - is very different to that of Muslims.
Dr Nazir-Ali said: "Dialogue should be on the basis of that difference. They appear to be saying 'this is what Muslims believe... if you agree, then let's have a dialogue'."
Christian leaders do now plan a response to the letter.
Professor Nayed insists that the dialogue must at least take place, arguing that world peace, even the survival of mankind, might depend on it.
He said: "Christians and Muslims make up more than half the world's population... and when you look at the weapons in the hands of those people... and the violence of terrorism, it's easy to see how dangerous it is for there to be so little understanding."