The father of the demon-possessed boy complained to Jesus about the inability of the disciples to cast the demon out. Jesus replied with a remark about the faithlessness of the present generation. It is possible that the disciples were the ones lacking faith, weakened perhaps by their pride in assuming they were invincible or that the power was their own. But it is also possible that the father was in large part to blame for the lack of faith. After all, he does confess to it. And he is in turn chastised by Jesus with those well-remembered words of encouragement that, after all, all things are possible for those who believe or trust in Jesus.
This concept of belief in the all sufficient power of God is also reflected in Isaiah 50:7-10. The Lord God can do anything. He can overcome any adversary and that includes Satan as well. But it is not the strength or action or even the faith of the person expressing the faith that is invincible. The sufficiency of the faith does not rest in the person expressing the faith, but in the object of the faith, Jesus. No problem or illness is too difficult for God to handle or remove Jesus proved by casting out the demon. He continues to do the same today by destroying the strongholds and works of the devil. Those who trust in Christ need have no real fear of that adversary as long as they cling to the strength of the Lord alone for help no matter the circumstances.