This is a sad commentary on the disciples. The father begged the disciples to cast out the illness (or demon) that afflicted his son, but they could not. In Luke 9:1, Jesus had clearly given the disciples authority over unclean spirits (demons). They had the authority to cast the demon out of the boy, but not the power. This story is related in Matthew 17, and that passage includes Jesus' rebuke of the disciples as well as a discussion between Jesus and these failed disciples. "Why couldn't we cast it out?" they asked. "Because of the littleness of your faith," Jesus replied.
We will look more at this tomorrow but for today, look at the rebuke Jesus gave them. "You unbelieving and perverted generation" he called them. The word translated as unbelieving is also translated "faithless". The word translated as "perverted" is not used here to indicate sexual deviant, but "twisted" or "turned away". Jesus was saying that, although He had equipped them with all they needed to heal the boy, they had turned away from the faith in Christ that would have been sufficient for the task.
How far away were they from their faith? A mustard seed's distance. Not far at all. It behooves us to stay close to our Lord. A task they had accomplished with ease on their journey was impossible when they moved away from their Lord just a bit. In fact, they were still right in the midst of the crowd. Still ostensibly close to Christ. An onlooker would not have been able to tell that they had moved away, but it became apparent when their power was gone
What a truth for us! We must be diligent to stay close beside our Lord, consistently and constantly faithful in order to have the power to accomplish the tasks God has given us. Perhaps this is the reason we see so little of the miraculous in our churches today, so little of divine intervention. We have the appearance of disciples, but not the power.
The words of Jesus could well be words for us today. "You unbelieving and perverted generation, how long shall I be with you and put up with you?" What is it we lack? Faith. We lack a mustard seed sized faith, and it separates us from the power our Lord would so freely give. Oh dear ones, step closer, move in, embrace our Lord and the life of faith He longs to give us.