Prayer is the walkie-talkie on the battlefield of the world. It call on God for courage (Eph. 6:19). It call in troop deployment and target location (Act 13:1-3). It calls in for protection and air cover (Mt. 6:13; Lk. 21:36). It calls in for firepower to blast open a way for the Word (Col. 4:3). It calls in for the miracle of healing for the wounded soldiers (Js. 5:16). It calls in supplies for the forces (Mt. 6:11; Phil. 4:6). And it calls in for needed reinforcements (Mt. 9:38).

This is the place of prayer – on the battlefield of the world. It is a wartime walkie-talkie for spiritual warfare, not a domestic intercom to increase the comforts of the saints. And one of the reasons it malfunctions in the hands of so many Christians soldiers is that they have gone AWOL.

God has given us prayer because Jesus has given us a mission…We are on this earth to press back the forces of darkness, and we are given access to the Headquarters by prayer in order to advance this cause. When we try to turn it into a civilian intercom to increase our material comforts, it malfunctions, and our faith begins to falter.

John Piper, The Pleasures of God, 214.