The theme of the Beatitudes is to show a felt need, then demonstrate how that need will see fulfillment in the kingdom of heaven.  The poor in spirit are blessed because they have no religion or spirituality to lean on, so (like the materially poor) they must lean more fully on Jesus to satisfy the righteous requirement of the law.  Therefore, theirs is the kingdom of heaven.

The second Beatitude promises comfort to those who mourn.

The Beatitudes identify several needs as virtues that ordinarily one wouldn’t think of as a virtue.  First the poor, now the mourners.  Next we’ll bless the meek and then the hungry!

So what’s up with prosperity preachers?  Are they not reading this section?  These guys say that you can have your best life right now.  Yet Jesus says to those of us in the present that you are blessed if you’re poor, in mourning, meek, and hungry — if you’re not having your best life now.

Suffering and trials will come.  If we lean on God in those trials and become closer to him, then we do well.  If we grow distant, if we let the trials create a rift between ourselves and our God, it is to our severe detriment.  God will deliver those who mourn:

The Spirit of the Lord God is upon me, because the Lord has anointed me to bring good news to the poor;  he has sent me to bind up the brokenhearted, to proclaim liberty to the captives, and the opening of the prison to those who are bound;to proclaim the year of the Lord’s favor, and the day of vengeance of our God; to comfort all who mourn; to grant to those who mourn in Zion— to give them a beautiful headdress instead of ashes, the oil of gladness instead of mourning, the garment of praise instead of a faint spirit; that they may be called oaks of righteousness, the planting of the Lord, that he may be glorified.  (Is 61:1-3)

And:

He will swallow up death forever; and the Lord God will wipe away tears from all faces, and the reproach of his people he will take away from all the earth,  for the Lord has spoken.  (Is 25:8)

Jesus once said that he is the Great Physician, come to heal the sick.  The well don’t need a doctor, right?  Conversely, those who do not weep have no need of someone to wipe their tears away.