I have heard or read many teachings on the Beatitudes, and all of them have included the idea that these were not only words of comfort, but directions for living. That we should seek to be poor in spirit, usually relating that to humility; that we should strive to be meek - same reason. The idea is that meekness is a quality that brings forth inheriting the earth, or that being reproached and persecuted is really a desirable situation which illustrates we are on the right track.
The current series for adult Sunday School had a rather different take. I haven't switched over to it, as it doesn't fit the whole picture of Matthew 5. But it's interesting, and I pass it along. It may at least fit some of the verses, specifically those which it has always seemed a stretch to include, involving some contortions of the ordinary meaning of words.
Jesus speaks of the least of the Kingdom of God as being greater than even the great of the world, including John The Baptist, greatest of all born to that time. He accentuates how blessed they are - even those who are downtrodden; even those who mourn, they're blessed; those persecuted people over there, you think of them as miserable, but if they are in the Kingdom of God they are blessed, more blessed than even the great of the earth.
This theory breaks down around the merciful, the peacemakers, the pure in heart - but for about half the beatitudes, it makes more sense than trying to work out why mourning is a good thing.