An excerpt from Darell Guder’s chapter, “Missional Witness,” in Missional Church:
In the Sermon on the Mount, blessings are granted to those who are poor in spirit (who know that they don’t have it altogether), to the meek (the gentle, the nonviolent, who leave vengeance up to God; see Ps. 37), to those who desire justice and righteousness, to those who show mercy and forgive, to peacemakers, and to those who are persecuted for the sake of righteousness and justice. These are the ones whose light will shine before all the world. They are the ones who will be like God in loving those who do not love them in return, who love and pray for their enemies, and who do not resist their oppressors with violence (Matt. 5:38-48). (p. 122)
Beginning on page 137, Guder again visits this sermon.
The dominant culture says, “You will be happy if you avoid any situation that exposes you to other people’s suffering or that causes you yourself to suffer or mourn or sacrifice.” This is the world of happy-face stickers and “Have a nice day.” On the contrary, Jesus pronounced blessing on those who mourn. God will comfort those who sorrow over the state of the world, injustices, oppression, their own sin, the sin of others, and the situations in which evil seems to have the upper hand. Those who grieve over oppression, who do not turn away from seeing it, will find comfort because God is going to do something about it, either now or, certainly, in the age to come. (p. 138)
For more on the Sermon on the Mount, here’s an essay by Walter Wink.