The bible is full of examples of intercessory prayer, of god's wrath being turned away by a devout word in the divine ear. In the episode of the Golden Calf (Exodus chapter 32), god apparently intended to destroy the Israelites for idolatry, but his judgment was altered by Moses' plea. Even Sodom and Gomorrah, those pinnacles of depravity from the book of Genesis, would have been saved had Abraham found ten or more "righteous men" there.
All of this, to my admittedly unqualified ear, sounds as if god could change his mind. The problem, so far as I can frame it, is this; in the typical Christian model of how things work, god is changeless, eternal, all-good, and all-knowing. As such, the whole idea of a person's prayer altering the course of what god wants is a little silly. God presumably already knows not only what is the best outcome, but knows what will happen; why on earth would the prayers of one person, or even of everyone on earth simultaneously, change that?
So, in my effort to understand this idea, I turned to C. S. Lewis. Even if I often disagree with Lewis' conclusions, I find him to be generally rational, and certainly a clear, sober-minded writer on the subject. Here's what I found:
Can we believe that God ever really modifies His action in response to the suggestions of men? For infinite wisdom does not need telling what is best, and infinite goodness needs no urging to do it. But neither does God need any of those things that are done by finite agents, whether living or inanimate. He could, if He chose, repair our bodies miraculously without food; or give us food without the aid of farmers, bakers, and butchers, or knowledge without the aid of learned men; or convert the heathen without missionaries. Instead, He allows soils and weather and animals and the muscles, minds, and wills of men to cooperate in the execution of His will...
I have seen it suggested that a team of people—the more the better—should agree to pray as hard as they knew how, over a period of six weeks, for all the patients in Hospital A and none of those in Hospital B. Then you would tot up the results and see if A had more cures and fewer deaths. And I suppose you would repeat the experiment at various times and places so as to eliminate the influence of irrelevant factors.
The trouble is that I do not see how any real prayer could go on under such conditions. “Words without thoughts never to heaven go,” says the King in Hamlet. Simply to say prayers is not to pray; otherwise a team of properly trained parrots would serve as well as men for our experiment. You cannot pray for the recovery of the sick unless the end you have in view is their recovery. But you can have no motive for desiring the recovery of all the patients in one hospital and none of those in another. You are not doing it in order that suffering should be relieved; you are doing it to find out what happens. The real purpose and the nominal purpose of your prayers are at variance. In other words, whatever your tongue and teeth and knees may do, you are not praying. The experiment demands an impossibility. (from an essay called "Does Prayer Work?")
Interestingly enough, such an experiment has been done, and not with "poorly trained parrots" but with entire church congregations who were honestly desirous of a positive result, despite Lewis' objections (and despite verses such as Deuteronomy 6:16, "Thou shalt not put the Lord thy God to the test."). A well-publicized experiment in 2006 called STEP (Study of the Therapeutic Efficacy of Prayer) tested the medical outcomes of over 1800 coronary bypass patients, who were sorted into three groups. Group 1 and Group 2 were both told they might or might not be prayed for; only Group 1 was. Group 3 was told that they would be prayed for (and were). The thirty-day serious complication or mortality rate was nearly identical between Group 1 and Group 2 (51% and 52%, respectively); Group 3 had a significantly higher rate of complications or death (59%).
I won't go into the possible confounding factors for the higher death rate among Group 3; what interests me is more how a Christian would explain why, if intercessory prayer works at all, Group 1 didn't show a lower risk of complications. "Thou shalt not put the Lord thy God to the test" sounds good, but my thought is, if ever there was an opportunity for god to show that what the Christians claim is correct, this is it. You would think that if presumably god wants people to believe, and to pray (and in fact Christians are positively commanded to pray, in a variety of places in the bible), some sort of results would have been forthcoming.
You get the impression that even Lewis was a little uncomfortable on this point. He said, "Prayer doesn't change God -- it changes me." Again, I have to wonder how this would work. How on earth would praying for something, to a deity whose mind I can't change, who knows what is "supposed to happen," and who will do what he chooses regardless, have any beneficial effects on me? Imagine a parent whose mind could never be swayed by his children's requests -- and telling the children, "You should ask anyway, because it's good for you."
While I am not religious (obviously), I can at least understand the concept of other sorts of prayer -- prayers for enlightenment, prayers for understanding, prayers for courage. But I really have no clue what the possible logic could be to praying for intercession, other than "the bible says we have to -- never mind why." Perhaps some reader will have a good explanation of it -- which I would welcome -- but on the face of it, it seems like the most pointless of pursuits.