In this point, Jesus was about to heal a demon-possessed young man at the request of his father. The disciples could not do it and the dad was losing faith. He had to ask Jesus to help his unbelief. Jesus healed the boy and then declared that the evil spirit can only come out through prayer. Meaning, that only looking to God, can we ever hope to accomplish his will. Not through our own means.
Next, Jesus reminds his duh-sciples again that he will die and then rise again on the third day. They don't get it. In fact, they ignore it and argue among themselves who is the greatest and try to hide it from Jesus. Jesus has to tell them that the rest of the world can fight for greatness. We as his followers are not to do that. Then Jesus took a child and said we have to be like that. Simple, believing, and obedient. Not naive or childish, but childlike.
This reminds me of someone who doesn't like to lose games. Often I will ask Tim to play a game with me, then he wins and I get mad at him. I want to be the greatest. I want to do things my own way and always win. But I must remember that I am not great. In fact, without Jesus, I am not enough.
I had to talk to someone who declared that she can't control her anger. Was she despairing or making excuses? I don't know. But I know that in my own power, I can't control my anger or my thoughts. I certainly cannot cure people of demons. But I need to constantly pray to the Lord for his guidance and even his control. He needs to change me so I think his thoughts after him and think less of myself. I am not enough, but he certainly is.