And after the mountain is gone, this tiny speck of faith just keeps on working, guaranteeing absolute success in every situation from then on. When Jesus met resistance to His healing and miracle power, He did not blame it on a lack of faith, but a presence of unbelief. The Scriptures tell us as much about ridding ourselves of unbelief as they do of increasing our faith. And he could there do no mighty work, save that he laid his hands upon a few sick folk, and healed them. Jesus was not referring to the demon in the young boy.
Rebellious unbelief comes from sin.
It openly defies the Word and power of God. The Exodus generation was guilty of this type of unbelief. When confronted with the promises of God, they hardened their heart and spoke out against God and Moses. This was not the kind of unbelief the disciples had when they tried to cast the demon out of the young boy. They were not hardening their hearts against God's plan.