“Prayer is the communication by which the weapons of warfare are deployed according to the will of God. Prayer is for war.
Let me show you this more specifically from John 15:16-17:
“You did not choose me, but I chose you and appointed you that you should go and bear fruit and that your fruit should abide, so that whatever you ask the Father in my name, he may give it to you.”(ESV)
The logic is crucial. Why is the Father going to give the disciples what they ask in Jesus’ name? Answer: Because they have been sent to bear fruit. The reason the Father gives the disciples the gift of prayer is because Jesus has given them a mission. In fact, the grammar of John 15:16 implies that the reason Jesus gives them their mission is so that they will be able to enjoy the power of prayer. “I send you to bear fruit so that whatever you ask the Father…he may give you.”
So I do not tire of saying to our church, “The number one reason why prayer malfunctions in the hands of a believer is that they try to turn a wartime walkie-talkie into a domestic intercom.”
— John Piper
www.desiringgod.org/conference-messages/prayer-the-work-of-missions