If prayers work in the way the OP suggests, then God is either weak-willed or capricious, neither of which is a comfortable thought. (I’m specifically excluding prayers-as-worship/praise and only discussing prayers-as-magic)
Imagine, for example, the following exchange:
Me: God? Why is my cat dying?
GOD: IT WAS THE CAT’S TIME TO GO AND I HOPE TO TEACH YOU ABOUT LOSS. IT’S PART OF MY PLAN TO BRING YOU CLOSER TO ME.
Me: But…I don’t want my cat to die!
GOD: THOUGH IT DOESN’T SEEM SO, MY SON, IT WILL BE GOOD FOR YOU AND YOUR CAT IN THE LONG RUN.
Me: Pleeeeeaaaazzzee?! Pleeeeeaaaaze?!
GOD: I’M SORRY FOR YOUR PAIN. I WILL HELP YOU GO THROUGH IT.
Me: Please, you who art in heaven, hallowed be your name. Please!!
GOD: OH. ALL. RIGHT. THE CAT LIVES.<pouts> BUT IF YOU DO THAT AGAIN, I’LL SMITE YOU.
Me: Kewl! It works! Hey God! Can I have an ice-cream cone?
**GOD: NO **
Me: Can I have an ice-cream cone?Can I have an ice-cream cone?Can I have an ice-cream cone?Can I have an ice-cream cone?Can I have an ice-cream cone?Can I have an ice-cream cone?Can I have an ice-cream cone?Can I have an ice-cream cone?
GOD: AAARGH! SHUT UP ALREADY!
Me: Please, you who art in heaven, hallowed be your name. Please!! Can I have an ice-cream cone?
GOD: FINE. HERE’S YOUR STUPID ICE CREAM CONE. <thinks>WHY DID I MAKE THEM SELF-AWARE? NEXT TIME IT’S PLANKTON ALL THE WAY.
I mean, c’mon. Either God has a plan, in which case praying for stuff won’t change anything (besides, your praying and/or lack of praying are part of The Plan), or God is just winging it, which is a scary thought or God is a wimp, which may be worse. (We won’t get into the “There’s no God” arguement)
Fenris