...prayer as a means of advancing God's kingdom is no stranger than any other means.
Go into all nations and preach the gospel, Jesus told his disciples, thus launching the missionary movement with its harrowing history; would not a large banner in the sky have served God's purpose as well? Heal the sick, visit prisoners, feed the hungry, house strangers - Jesus also commanded these activities, delegating them into our hands rather than enlarging his own Galilean ministry to global scale.
Consistently, God chooses the course of action in which human partners can contribute most.
Prayer: Does It Make A Difference? by Philip Yancey, page 137