So here we are, the famous Sermon on the Mount. Jesus' words are so familiar and yet so debated. Should "blessed" be translated as "happy"? Who are the "poor in spirit"? Should it be translated "the poor" as in Luke's Gospel? And why does he say it is blessed to mourn? Mourn our own sin? Mourn the suffering in this world? And on it goes.
Frankly I'm not sure what the answers are to all these little debates, but I don't think it's necessary to have them all settled to get what Jesus is saying. The big picture is clear. Jesus is describing a way of living that is completely contrary to the values and attitudes of this world. He is saying that those who live in this un-worldly manner are really living for the world to come.
If you focus on the large contours of Jesus' description of blessedness, a picture begins to form. Think of what it means to be poor in spirit, mournful, meek, pure-hearted and peaceable; to exercise mercy, crave true justice, and be hated and persecuted for following in that path. That kind of person isn't going to get ahead in this life. It means stopping to help others instead of pushing to get to the front of the line; giving away your time and money so that there's hardly any left for yourself. It means choosing to hang with the people that nobody cares about rather than networking with the movers and shakers who are "going places." Are you a loser or something? Why aren't you promoting yourself, selling yourself, taking charge, fighting back? That's all you hear these days, right? The whole message of the world is to grab all you can while you can. The whole of Jesus' message is to surrender everything you have in service to others.
These blessed ones Jesus talks about are willing to give so much because they aren't invested in this world, they're looking to the next. There they'll receive their true inheritance. They will find everlasting comfort, satisfaction, mercy, and sonship in the presence of their true Father. They see a direct connection between the mercy they show in this life and the mercy they will receive in the next, between the righteousness they crave in this life and the satisfaction they will receive in the next. It's like they hear a song that's playing from that other world and they are continually drawn toward it, in spite of the cacophony of this world, in spite of everyone else saying, "Song? What song?" as they walk around with their hands over their ears. They might even get persecuted for talking about the song too much, in which case Jesus says, "Rejoice and be glad, for your reward in heaven is great."