Taken from the gospel of Matthew 17:19-21, when Jesus is asked by his disciples, 'why could we not cast out that demon'? Jesus explains that if they had faith the size of a mustard seed, they would speak to the mountain, and the mountain would remove.  At face value such an explanation is a paradox (a seemingly absurd or contradictory statement which when investigated may prove to be well founded or true).  The preacher is encouraging the believer to reclaim the simple faith that saves, the simple faith that sets the captive free.