Does Prayer Matter by Philip Yancey?
All the passages below are taken from Philip Yancey’s book “Grace Notes—Daily Readings with a Fellow Pilgrim,” published in 2009.
After surveying Jesus’ practice of prayer, I realize that his example does answer one important question about prayer: Does it matter? When doubts creep in and I wonder whether prayer is a sanctified form of talking to myself, I remind myself that the Son of God, who had spoken worlds into being and sustains all that exists, felt a compelling need to pray. He prayed as if it made a difference, as if the time he devoted to prayer mattered every bit as much as the time he devoted to caring for people.
A physician friend of mine who learned I was investigating prayer told me I would have to start with three rather large assumptions: (1) God exists; (2) God is capable of hearing our prayers; and (3) God cares about our prayers. “None of these three can be proved or disproved,” he said. “They must either be believed or disbelieved.” He is right, of course, although for me the example of Jesus offers strong evidence in favor of that belief. To discount prayer, to conclude that it does not matter, means to view Jesus as deluded.
Jesus clung to prayer as to a lifeline, for it gave him both the guidance and the energy to know and do the Father’s will. Even then he sometimes grew exasperated with his earthly surroundings (“0 unbelieving generation, how long shall I stay with you?”), sometimes fought temptation (“Do not put the Lord your God to the test”), and sometimes doubted (“My God, my God, why have you forsaken me?”).
Skeptics raise questions about prayer’s usefulness: If God knows best, what’s the point? To such questions, I have no better answer than the example of Jesus, who knew above any of us the wisdom of the Father and yet who felt a strong need to flood the heavens with requests.
Although Jesus offered no metaphysical proofs of the effectiveness of prayer, the very fact that he did it establishes its worth. “Ask and you will receive,” he said frankly, a rebuke to anyone who considers petition a primitive form of prayer. When his disciples failed in their attempts to heal an afflicted boy, Jesus had a simple explanation: lack of prayer. 
Prayer: Does It Make Any Difference? (79-81)