The main way that God deepens, strengthens and awakens confidence in prayer is not through answered prayer. It's by the word of the living God! When God says, "I hear you," we should believe him.
So when my confidence in prayer languishes and I feel like, "Why spend 10 or 15 more minutes here?," my strategy for rebuilding my confidence is not to catalog all the answers. One of the reasons for this is that they're all ambiguous, even the biblical prayers.
If you're skeptical enough you can always say, "It would've happened anyway." Always! It can be something absolutely stunning, like if you were praying over a tumor and it shrank under your hand. "Well, it was ready to do that anyway." You cannot get confidence if there is a skeptical voice inside of you constantly saying, "Answers don't do it because they're all ambiguous."
So if you base your confidence in prayer on answers to prayer, and you have a heart that is always wondering, you'll never have confidence. And I think I have that heart! I'm a really skeptical guy! I hear some story about an amazing healing and my first thought is, "Got some doctor records?" That's the way I'm wired! So if I'm going to keep praying and believing prayer, it's going to be through Jesus getting in my face and saying
Which one of you, if his son asks him for bread, will give him a stone? Or if he asks for a fish, will give him a serpent? If you then, who are evil, know how to give good gifts to your children, how much more will your Father who is in heaven give good things [or, as it says in Luke, the Holy Spirit] to those who ask him! (Matthew 7:9-11)
Now that's Jesus getting in my face and saying, "You couldn't believe me. I'm telling you that if you know how to give your child something good, your Father does it too!"
So I think at that point you pursue it a little further and say, "OK, I trust you Jesus. I believe you." And then you let your heart go on this Father idea. And you go to other texts in the Bible where he is called your Father. And you see that you are therefore his heir, and he loves his children. He will always do good for his children, and he wants his children to ask him for things!
And so if you go to enough passages of Scripture where God is telling you how inclined he is to your prayer, you either are going to throw the Bible out or you are going to start growing in confidence: "God hears me! God hears me!"
I'll give you an example just from this morning. I was praying this morning for my children and for myself from Ephesians 3:14-19, where it says,
For this reason I bow my knees before the Father, from whom every family in heaven and on earth is named, that according to the riches of his glory he may grant you to be strengthened with power through his Spirit in your inner being, so that Christ may dwell in your hearts through faith—that you, being rooted and grounded in love, may have strength to comprehend with all the saints what is the breadth and length and height and depth, and to know the love of Christ...
And I stopped. I have prayed that for myself hundreds of times. Hundreds. And it hit me. I've been praying this prayer for 29 years at this church, that God would grant me to know the height and depth and length and breadth, the love of Christ that passes knowledge. And do you know what came into my mind? "That's the reason you have seen what you have seen about the nature of the love of God being the glorification of himself in people's lives."
My way of talking about the love of God today is that you are loved, not when God makes much of you, but when he, at great cost to himself, gives you the inclination to make much of him and the joy of making much of him.
I do not believe I would have seen that if I had not prayed that prayer a hundred times. So now, of course the skeptic would say, "I think you would've thought of that even if you hadn't prayed that prayer. I think you would've seen that in the Bible and you would've taught it even though you hadn't prayed that prayer." To which I would say, "I guess that's what you're going to believe. But this morning at the bottom of my soul it seemed to me that God was saying, 'The reason you see what you see is because you've asked to see it a hundred times. I've heard you. It's no accident that you've seen John 11:1-6 in relation to John 17:1-5, and 24 the way you do. I don't give everybody that. I give it to you. I give it to a hundred others, thousands of others. I give it to people who want it so bad. They pray Ephesians 3:14-19 over and over and over and over. And I store it up in a bottle, and then one day in a conversation with somebody or while you're studying the Bible I pour it out, and you see what you would not have seen.'" That's the way it works for me.
So I get subjective confirmations like that. I can't prove them. And if you're mathematically oriented, demanding proof, you won't ever get it. But if you're desperate to have help, God will give you the help; and he will show you along the way, from time to time, "I gave you that help. I gave you that help. The only reason you're a believer still is that I gave you that help."
-John Piper (original here)