We pray because Jesus prayed. A simple enough answer. Christians follow Christ. The Bible records more than a dozen of Jesus' specific prayers as well as his teaching and parables on the subject. We can see that it was his practice to pray regularly and for long periods. Five times the Gospels mention his practice of praying in solitude. He prayed in the Garden, he prayed on the cross. He seldom prayed for himself. The request that this cup be taken from him is perhaps the only occasion and that was modulated by "not my will, but thine." He often prayed for others: for children brought by their mothers, for the people by the grave of Lazarus, for Simon Peter whom Satan sought to sift, for those who were crucifying him. At times of special importance he intensified his prayers: at his baptism, all night before choosing his disciples (was it Judas that gave him so much trouble or was it Peter?), on the Mount of Transfiguration, and especially before his death. His prayer could be exuberant as when the 70 returned from their mission. He prayed that his disciples would receive the Counsellor; he prayed in his great High Priestly prayer of John 17 for all of us believers who would come after him.
Did he get everything he prayed for? Do we? The answer is no, or at the best, not yet. When I said he prayed for us, what did he pray for? He prayed for unity. "That all of them may be one, Father, just as you are in me and I am in you." At the last count there were 34,000 distinct denominations and sects. Is that an answered prayer? Much as I dislike ECUSA and all that they stand for, you can see where Rowan Williams is coming from and why he prays for unity. We should pray for the Anglican Church that they will come home to Christ.
I suggest that on that long night before he chose the twelve, he prayed for Judas. He certainly prayed for Peter, that his faith would not fail. We know that Peter's faith failed him three times before the cock crowed. The Bible tells us that Satan has asked to sift him like wheat. As for Judas Luke tells us that 'Satan entered Judas'. We are in a spiritual warfare. We face supernatural forces. Sometimes Satan wins the battle. We know that he is a beaten foe, but he won't lie down just yet. He means to take as many casualties with him as he can.
Like his ancestor Jacob before him Jesus wrestles in prayer. We must do the same. Prayer is hard work. Despite our wish to be spared Satan's attacks God permits them. We cannot fathom that. Why was Satan permitted to smite that good man Job? Why didn't Jesus restrain Satan when Peter slunk into the courtyard and warmed bis hands by the brazier? He was bravely there when others had fled. Why wasn't he protected? And Judas? Poor Judas. Jesus' friend and companion those three years on the road. Why would he not spare his friend from this harrowing? Why did he allow this evil possession?
We know now why. We know why Jesus died. It seemed a cockeyed plan at the time, but Jesus had to die. He had to be betrayed. He had to be denied. No rescue plan could be allowed to interrupt the proceedings. The just must die for the unjust. There was no other way. There was no other good enough. God knew what He was doing.
We may be perplexed at God. Why doesn't He answer my prayers? Why doesn't He do what I want? Prayer reconciles us to the will of God.
If He is going to do what he wants anyway, why should we pray? I don't know. I only know that in some mysterious way his plans are accomplished because we pray. How do I know? Because Jesus prayed and even though his prayers appeared not to be answered, God's will was accomplished and millions were saved.