The letter of the Islamic scholars is certainly a step forward, but I am a little concerned about the idea that we worship the same God. It is too easy a phrase, one that trips off the lips of modern man. Certainly Muslims and Christian worship one, omnipotent, eternal God, the source and origin of all things.
We Christians worship a God who is so great that he contradicts what we perceive as His own nature. The God who is outside of time and space through the womb of the Virgin Mary steps into time space. This is beyond the Muslim concept of God, for them God cannot humble himself. His involvement with mankind is only through an intermediary, a prophet. Though he might know all about mankind, and indeed every man, he cannot share the experiences of Man. In Jesus we see God as sharing all that man is, his birth and death, even his descent into Hell. For the Jews this was a stumbling block for the Greeks it was folly, but for Christians it is Salvation.
Even when we Christians speak about worshipping the same God I get a bit uneasy, there is always a tendency, certainly amongst Protestants to broaden the gap between God and man. Grace, for them, is something that is irresistible, therefore man's co-operation is unnecessary, hence the downplay of Mary's fiat. God "needed" her co-operation, and does "need" ours for our salvation.
The Reformers of the 16th century did everything they could to deny the efficacy of the sacraments, the continued involvement of God in the Church and in human history. They wanted to distance God from man. I find it incredibly significant that the draconian Poor Laws came into England, whipping the poor from parish to parish, on the rump of the reformation, as of course did deepening illiteracy, a greater gulf between the peasantry and the aristocracy; think of Luther's war against the peasants, and the unemployment and consequent starvation that followed the Reformation.