The grain of mustard seed is used to describe the Kingdom of God.  Jesus also said that if we had faith the size of a mustard seed that we would be able to move a mountain.  Now in the parable of the mustard seed, the seed obviously starts out small and insignificant but grows to a large plant.  Maybe we can compare our faith growing in much the same way.  It’s sort of like all that grass growing out in my yard.  It once started out as a seed, just sitting there it could do nothing on its own, but when it was planted it grew.  Now just one blade of grass in my yard wouldn’t do too much for it, but there are thousands of blades of grass out there.  they are so ‘productive’ that I need to have the grass mown at least once every two weeks or it would become nearly impossible to mow.  I suggest that we don’t cut down our faith in the Kingdom of God, but let it grow til it is impossible to cut down.