I do believe prayer can have an affect on our world. People often ask how prayer can change anything if God already has history pre-determined. Someone described it to me once as being like a stage play. There is a pre-determined storyline and lines the actors have to speak.
But they are allowed to ad-lib here and there if they want to. Ultimately, the story starts and ends the same, but the little details in between can be altered slightly to the wills of the individual actors.
So when we ask for something that doesn't alter God's ultimate "storyline", He may allow us that thing we ask for. It may seem to be a significant development in the story at our level, but from God's perspective, it's just one slightly altered line in the vast epic of history.
Having said all that, I do believe I have seen answers to my prayers plenty of times. This past summer I was suffering a horrible eye condition that at times left me almost blind in one eye and in excruciating pain constantly. It would hit me with zero warning and kept re-occurring over and over again for months. I began to lose hope because it really seemed like I would have this the rest of my life, and online testimonials seemed to
affirm that fear...
I asked God why He was having me go through this, as I had already endured a different kind of eye condition as a child and therefore didn't take my eyesight for granted at all. I wondered if He had something to teach me and asked Him to show me what that thing was.
Long story short, the pain and fear was what it took to get me back to doing daily devotions, which I had all but given up for over a year. When you are suffering like that,
any word from God is precious and comforting, so I was desperate to hear from Him.
I ended up turning to a passage which seemed to clearly indicate an area of my life with which God was not happy, and an area which I already knew I was borderline unrepentant... The next morning, I turned to another passage where God was expressing His love to His people and that despite their rebellion, He had decided to heal them and be close to them again.
I had gone to the eye doctor and they tried one procedure which seemed to work at first, but then the pain came right back which was very discouraging. So they tried a different treatment and I once again waited it out to see if the pain would finally go away. The same day that I read about God promising His healing, I was at work when suddenly my affected eye felt like there was a cool breeze blowing on it. I had another appointment that evening, and the eye doctor said my eye was 99% healed! I actually was trying not to laugh the whole time, because I knew that was what she was going to say! When I felt that coolness on my eye, I just... knew.
I really do believe that God heard me crying out to Him in my pain. But it wasn't like He just healed me and there was no cost. I was forced into a place of repentance for a sinful behavior I had been engaging in, and I had to address that behavior before the healing happened.
So that's my story.