What Does it Mean to be Blessed?

The Sermon on the Mount, a collection of Jesus's teachings, opens with the Beatitudes.  Jesus has called people to follow him.  But what is the substance of that following?  What is the nature of Jesus' mission?  Jesus climbs up a mountain, sits down in the posture of a teacher - on of Matthew's most cherished images of Jesus - and instructs his followers on the shape of his kingdom.  Jesus's reign is characterized by blessing.  Before there are ethical instructions, certainly before there are any exhortations, there is blessedness.