Prayer is a powerful weapon. Why am I saying this? As the Hospital chaplain, I was going around the male ward at our hospital, and I met with a Muslim believer after talking and encouraging him with the word of hope, I had to ask his permission to pray with him but he refused and said we don't belong to the same faith and I cannot take your prayer rather I ask the Sheik to come and pray for me.
After I finished visiting the sick I went back to my office, and I had to close the door and prayed for the guy who refused my prayer. The next morning I pass by his bed and greeted him, this happened for about 4 days. The other morning when I greeted him he called and asked me to pray for him as he was about to be sent to the theater for an operation and we prayed together. To make the story short, after his successful operation, he came to my office one day and said to me "Man of God, now I have realized that your God is not a selective God he can even listens to anyone."
Then I said to him, He is God of all human race; at this moment I saw the power of prayer.