Some thoughts from N.T. Wright in The Challenge of Acts:

“Now of course: prayer remains a mystery. We don’t understand why sometimes new things happen through prayer while often they seem not to. We don’t understand why the church prayed for James and Herod killed him, and the church prayed for Peter and he got out of jail free. But Jesus himself and the early Christians urged us to persevere in prayer; and you only tell someone to persevere in prayer if you know it will sometimes be hard. The battle is on. We won’t see the whole picture; we have to hold our bit of the line.”

There are things that can happen in prayer that simply don’t if we do not pray. Prayer somehow creates the possibilities.

“There is a reason why, in many traditions, including mine, ministers and clergy say what we call the Daily Office. You never know what new purposes and possibilities are waiting in the wings. But if you step out of the great river of prayer you may just never see them.”