Now the Bible does tell us to expect answers to prayer when we pray according to God's will. Part of prayer is actually discovering God's will. But this does sound like a complete cop out, doesn't it... if I pray for something and it's answered, then that must have been God's will; but if it isn't answered, oh well, it clearly wasn't God's will. But in fact, God is not capricious, and His will can be known. He's revealed His will in the Bible. His will is for people to believe and trust in Him, and for His people to live righteous lives. But to be healed from all sicknesses? In a sense that is His will, though not for the present. God has said that He will take away sickness and disease in the "New Earth" after He returns. But in the present we are still to suffer these things. So I think that if you want to understand how prayer is supposed to work, you need to read your Bible to discover God's purpose for prayer, and to discover God's will. I can certainly testify to the effectiveness of prayer in my life when I've prayed for the strength to resist temptation to sin, or when I've prayed for the ability to share the gospel with others. On that latter point, for example, I have experienced many times when unbelievers have asked difficult and challenging questions, and it has been nothing short of a miracle that I've understood how to answer them on the spot.
Sometimes the way we think prayer should work is misguided. The television program "Glee" gives us an apt illustration of this. In the episode "Grilled Cheesus", Sue is opposed to God because as a child she was grieved by the cruelty people showed toward her sister, Jean, who has Down's Syndrome. Her prayers as a child to heal her sister were never answered, and so she, like many others, considers prayer a false hope. At the end of the episode, however, Sue is sitting with her sister, Jean, and asks her if she believes in God, and explains how she doesn't believe in God because of the cruelty she witnessed towards Jean. But Jean replies, "God never makes mistakes; that's what I believe. ... Let me pray for you, Sue?"
Now, I don't know whether the writer intended to convey this message, but I think this episode shows us the error we often have in our attitude towards prayer. Sue saw a problem and she saw a solution... her sister was experiencing cruelty because of her condition, and the solution, in her mind, was to heal the condition. Well, that's human wisdom. But we cannot be upset with God because He's wiser than we are! No, I watch this episode and consider that God did hear Sue's prayers, and understood the concern she had in her heart for her sister. But His solution, rather than to heal the condition, was to give Jean faith in Himself, and that faith would allow her to endure that cruelty! This is a far more Biblical expectation than for Jean to have been healed of her Down's Syndrome. As I said before, God's will, as He has revealed it in the Bible, is for us to believe and trust in Him. And this is why I say that part of prayer is actually discovering God's will. When we pray, we need to ask ourselves whether we're praying according to God's will as it has been revealed. Are we praying with Biblical expectations?
For everyone who asks receives, and the one who seeks finds, and to the one who knocks it will be opened. What father among you, if his son asks for a fish, will instead of a fish give him a serpent; or if he asks for an egg, will give him a scorpion? If you then, who are evil, know how to give good gifts to your children, how much more will the heavenly Father give the Holy Spirit to those who ask him! (Luke 11:10-13)