The Inglorious Reward (Mark 9:14-29)

You would think that after showing the glory of heaven to the disciples that there would be great joy in this. Finally, a kingdom that they could embrace, and see.  A kingdom that manifests the glory of the Lord.  However, this is not how the kingdom is manifested with the disciples at all.  So, why is it in the midst of what appears to be the disciples flailing that the kingdom is still working?  Why does Mark include this story in HIs narrative?