Blessed, Pt. 6: Pure in Heart

Of all the Beatitudes, the statement of Jesus about "the pure in heart" may be the most difficult. It isn't hard to see ourselves as spiritually bankrupt, mourning, meek, hungering and thirsting, merciful, peacemakers, or even being persecuted. But being "pure in heart"? Probably no one goes around thinking of themselves as being pure in heart. So what does Jesus mean and how can we pursue this "purity of heart"?