When tomorrow never comes

Although I don't think unanswered prayer casts doubt on God's existence (too much evidence for that), it does cast prima facie doubt on God's benevolence. Ironically, Deists think the problem isn't with unanswered prayer but answered prayer! They think a God who intervenes is a God who lacks foresight to get it right the first time around. They view divine intervention as God rewriting the script. Editing his rough draft. That's actually a good objection to open theism. 

In theory, this ranges along a continuum from a God who never answers prayer to a God who always answers prayer. What would a world be like where God answers every prayer? 

To begin with, are we confining that to Christian prayers and pre-Christian Jewish prayers? Or does that extend to, say, Hindu prayers? Even if we confine it to Christian and Jewish prayers, do we distinguish between nominal believers and true believers? 

One problem with God answering every prayer is that some prayers cancel out other prayers. Some prayers are mutually incompossible. 

We might compare efficacious prayer to time-travel scenarios. In the sci-fi lore, time travel has a disruptive impact on the future by replacing the original future with an alternate timeline. The more often that happens, the more disruptive the effect. Cumulative temporal dislocation. 

Imagine a world in which there was no time-travel from January until the first Thursday in July. Up to that point there's continuity as people cycle through the week, a day at a time. But on the first Thursday in July (of that year), time travel became ubiquitous. 

That means you never get beyond Thursday. Friday never comes because Friday is constantly replaced by alternate futures. Every morning, when you wake up, it's Thursday. Each time it's a different Thursday. Not a different calendar date Thursday. The same calendar date Thursday, but a Thursday in a different timeline. You go through Thursday, go to bed, fall asleep, and it's Thursday all over again when you wake up because the disruptive effect of ubiquitous time travel resets the starting-date. 

Efficacious prayer would have a similar effect. Two alternate timelines sharing their histories up to the moment where they fork off. If God answers a prayer, that stands in contrast to what might have been had he not, and vice versa. If God answered every prayer, that's like constantly resetting the starting-date–so that we keep repeating the same calendar day. Different things happen each time because it represents a road not taken, but there's no continuity and no progression. You're forever stuck in Thursday. It's not the same as a time loop, because things change every time that happens, but it's always on that particular day. The next day never comes. Hence, the paradox of efficacious prayer. 

If efficacious prayer generates a conundrum like that, then that may be one reason why God selectively answers prayer, even though some prayers seem to be just as "deserving" as others. God strikes a balance between stability, intercession, and chaos.