After his first announcement, the disciples misunderstood. They couldn't see how a "messiah" would be killed; they expected a show of power. Thus, Jesus taught a true understanding of him would result in denial of self and the carrying of a cross (the disciple would learn the way of sacrifice). Now, the identity of Jesus is made even more clear -- "This is my Son! Listen to him!" -- and his role is established -- if Elijah has already come, we are in the "last days" of the day of the Lord, and judgment is coming.
This brings about a dispute over faith. In the face of identity and mission, we must ask whether we truly believe Jesus. Are we like the disciples, looking for something other than Jesus, or are we disciples who deny ourselves to follow him? In the dispute over faith, Jesus encounters a man who has a boy who is possessed by a demon. The disciples are unable to help. Jesus then bemoans the lack of faith in this generation. Jesus calls the man to faith -- to faith that is greater than comprehension or what can be controlled. The man is a model of the kind of reaction that disciples should have. He has faith, but recognizes he needs more faith, and calls upon the Lord (Jesus) to help him with this!
This should be a daily cry for us: Lord, I believe; help my unbelief! Unbelief, in this context, is not discerning Jesus properly. This becomes clear in the next unit: Jesus announces his upcoming death and resurrection for the second time. But the disciples "unbelieve." They argue about who is greatest. So Jesus pulls them aside and tells them, if they want to be first, they have to become last of all; they need to become like children. Will the disciples learn? Will we?
Churches are places where control and power come to the forefront. Sadly, many churches create a vacuum where these things can fester. People who should not be in leadership, and wouldn't be in any other organization, tend to end up in positions of leadership in churches. Such people can be very destructive. It is up to each disciple to properly discern Jesus, to deny self, and to become a servant of all.