Prayer is not a domestic intercom

I preached yesterday in my series through the gospel of Luke on the first 13 verses of chapter 11. In that passage, Jesus teaches His disciples to pray. To follow on that sermon, here is what I consider a most helpful quote from John Piper in his book Let the Nations Be Glad!:

Probably the number one reason why prayer malfunctions in the hands of believers is that we try to turn a wartime walkie-talkie into a domestic intercom. Until you know that life is war, you cannot know what prayer is for. Prayer is for the accomplishment of a wartime mission. It is as though the field commander (Jesus) called in the troops, gave them a crucial mission (go and bear fruit), handed each of them a personal transmitter coded to the frequency of the General's headquarters, and said, "Comrades, the general has a mission for you. He aims to see it accomplished. And to that end he has authorized me to give each of you personal access to him through these transmitters. If you stay true to his mission and seek his victory first, he will always be as close as your transmitter, to give tactical advice and send air cover when you need it."

But what have millions of Christians done? We have stopped believing that we are in a war. No urgency, no watching, no vigilance. No strategic planning. Just easy peace and prosperity. And what did we do with the walkie-talkie? We tried to rig it up as an intercom in our houses and cabins and boats and cars -- not to call in fire power for conflict with a mortal enemy, but to ask for more comforts in the den.