If you want to wake someone up from his sleep, all you need is an alarm clock or a rooster or a tap on his shoulder. But a person who is not aware of God's existence is often a lot more difficult to wake up. I recall in Mark 9, Jesus drove out a mute and deaf spirit out of a boy after his disciples had failed to do so. Later, they asked him why they could not do it. He said to them that that kind could only come out through prayer. In our case, prayer is absolutely needed to wake up someone who is spiritually asleep.