Prayer is the central activity of spiritual warfare. 

Spiritual Warfare: the ongoing battle between the church and the Devil with his angels. It is waged by holding faith and a good conscience, and prayer. 

Prayer: the act of communicating with God as an expression of trust in Him. Calling on God to come through on His promise. It is both a confession of dependence on God and a cry for relationship with Him. It's the means by which we grow in Him. Prayer is a mark of a healthy church (Acts 2:42). Prayer is God's prescription for life in a fallen world. 

In prayer, God allows us to be involved in eternally important activities, because God answers prayer. 

Because prayer is so powerful and important, Satan attacks it in 2 ways: 1) Idolatry of the self, and 2) Sin: a lifestyle of habitual, unconfessed sin as individuals or a church that tolerates open unrepentant sin within it. (1 Pet. 3:7; Ps. 66:18; Isa. 59:2; James 4:3).