He will fill them and transform them into sons and daughters who inherit the land"
As Jesus began his ministry, he called people to "repent, for the kingdom of heaven is at hand." In the beatitudes, which means "blessings," Jesus is proclaiming the blessings of that Kingdom. He himself is the fulfillment of a new covenant that he promised through his prophets, and the perfection and realization of a new glorious kingdom.
This is a Kingdom that you cannot take by force or perfection or ruthlessness. Instead, this upside down Kingdom is one in which the peacemakers, the hungry and thirsty, the meek and the broken and the persecuted will receive. Jesus will give them mercy and comfort. He will fill them and transform them into sons and daughters who inherit the land, rulers who will see God and reign in the Kingdom. His blood and His lordship is our way into that Kingdom.