Is worldwide coordinated prayer effective?

Reading about the pope making September 7th a day of fasting and prayer for peace in Syria ....

[...] September 7 is the vigil of the birth of Our Lady, Queen of Peace”. Christians know that, as Jesus said, some intractable problems can only be healed by fasting as well as prayer; fasting is an ancient tradition, not much in evidence these days outside the dieting industry, where it waxes and wanes in popularity, but still a powerful sign of sorrow, repentance and a serious commitment to the particular prayer intention. The Holy Father concludes his appeal with an invocation to Mary, Queen of Peace, that “she [may] help us to find peace” because “all of us are her children”.

So often in our personal lives we Christians know that it is only through prayer that seemingly insoluble situations are resolved. As the Pope indicates, we also have a responsibility for the wider society, in this case for Syria, because “all men and women of good will are bound by the task of pursuing peace.” So we are obliged to do something and not merely wring our hands.

This reminded me of Jim Wallis in 2007 asking people to pray en masse for Congress to end the Iraq war, and I realized something about myself back then, and I feel the same way now - I guess I don't think coordinated prayers and fasting will make any difference as far as getting God to fix things. It's not that I don't think he fixes things, but I find just creepy the idea that he bases his willingness to intervene on numbers or on ritualized self-denial .... surely none of us think God's just waiting around for an adequate asking before he'll work for peace? But maybe this isn't about God, but about people - maybe the pope hopes this will raise people's awareness and get them to do something practical about the situation, or that it will alert leaders to a general wish for peace?