Matthew tells us in chapter 5 of his gospel concerning Jesus "Seeing the crowds, he went up on a mountain, and when he sat down, his disciples came to him. And he opened his mouth and taught them...." This begins what is often referred to as The Sermon on the Mount. It is in this sermon that we hear Jesus repeatedly say "You have heard that it was said....but I say to you..."; again and again Jesus references a command of Jewish law only to add to it an even more strict command. "Don't murder? Of course! But don't be angry either. Don't commit adultery? Don't even lust!" Scholars tell us that Matthew's portrayal of Jesus ascending a mountain and speaking a new law is meant to remind us of Moses who ascended Mt. Sinai and received the Law from God. Matthew is using the example of Moses to help us understand who Jesus is. Jesus is the new lawgiver, or more precisely, Jesus is the lawgiver he has always been because he is the God who gave the law to Moses on Mt. Sinai who has now taken on human flesh. He is the one who will "fulfill" the law as he says in v. 17.
But Jesus "fulfilling" of the law seems to take it to a level that is impossible to keep. Not only does Jesus command us not to be angry and lustful. He also says "that everyone who divorces his wife, except on the ground of sexual immorality, makes her commit adultery". And later he says "You have heard that it was said 'An eye for an eye and a tooth for a tooth,' But I say to you, Do not resist the one who is evil. But if anyone slaps you on the right cheek, turn to him the other also. And if anyone would sue you and take your tunic, let him have your cloak as well." Jesus then sums up this new commands by saying "You therefore must be perfect as your heavenly father is perfect."
Jesus can't be serious about this, can he? Divorce and re-marriage is adultery? Don't resist evil and violent people? Be perfect? Surely Jesus realizes that he is asking the impossible, right?
I actually think Jesus does realize the impossibility of what he is commanding in these verses... though probably not in the way we might expect. Objections to the idea of living out the Sermon on the Mount almost always stem from the impractically of such a life. "Lust and anger are just part of being human. How can two people who are miserable stay together? Doesn't Jesus know what would happen if we didn't fight back against evil people? That's just not how the world works!" And so Jesus is written off as an idealistic dreamer (or in significant portions of the Christian tradition as the giver of the impossible law which drives us to his mercy).
I think Jesus knew quite well that his words in the Sermon on the Mount didn't describe the way the world works. In fact, I think he knew it so well that he knew the workings of the world would result in his own crucifixion. In the world as it stands, the commands Jesus gives would indeed be impossible which is why I believe Jesus is doing more in the Sermon on the Mount than giving a "new law". Jesus is announcing a new world.
I believe that is what Jesus is doing in the verses commonly called the Beatitudes (Matthew 5:3-11). We often approach these verses as if they are law as well. We interpret them to mean that if we want to be blessed then we must be poor in spirit, mourning, meek, merciful, pure in heart peacemakers who hunger and thirst for righteousness. So we make the Beatitudes a list of Christian virtues. But these verses are not imperative. They are indicative. Jesus is not commanding anything. He is proclaiming.
In fact, Jesus is proclaiming in these verses things that seem to be contrary to reality. Those who mourn are blessed? The poor, the meek, and merciful are blessed? It seems those are precisely the kind of people who aren't blessed in our world; the kind of people who are constantly taken advantage of. And again, that's precisely the point! Jesus isn't describing the way the world works. Jesus is describing how his renewed world will work. Jesus isn't describing the kingdoms of the world. He is proclaiming his own kingdom; a kingdom that turns power and influence upside down, a kingdom where those who mourn will be comforted and those who are merciful will be shown mercy. This is not command. It is promise. The beatitudes are Jesus' promise that the world will not always be as it is now; that might will not always make right, that the weak will not always be mistreated but that one day Jesus will rule over a kingdom marked by genuine justice and peace, a kingdom where the not-so-blessed of this world will be blessed.
But in the meantime, in this time between the times, in the tension of the "Blessed are...for they will be...", Jesus calls upon us to to be a community where the impossibility of the Sermon on the Mount becomes a reality. Not because we are especially moral people who try harder. Not because we've discovered that Jesus' commands are really practical after all. But because of the resurrection. Because the one who gives this law is also the one who accomplishes our Exodus. Because in the raising of Jesus from the dead, God has said "Behold, I am making all things new." Because the Spirit that raised Jesus from the dead is able to make us new as well. Because we believe there is a kingdom that is coming that doesn't play by the world's rules and that kingdom is already being made a reality in us. Because we are by virtue of what we will be.