5:17 "Think not that I have come to abolish the law and the prophets; I have come not to abolish them but to fulfil them.
Interesting, I was thinking about this passage earlier this week. I have heard people in Jewish circles say that "abolish the law" and "fulfill the law" are Jewish idioms. Whether or not that's true, or just what they're taught these days (which is not always what was taught in the past) - I find it interesting to dwell on. Supposedly, to "abolish the law" meant you were mis-interpreting a passage. To "fulfill the law" meant you were nailing it right on.
So we look at it this way - in Matthew 5, Jesus gives the beatitudes. He then gives his audience some advice - not to hide from the world what God has given in you. Then we come to this verse, which starts a discourse on obedience to the law, and the demand of righteousness for entering heaven. Jesus is basically assuring his audience that the law still has a purpose, and uses this verse to affirm his authority on the law.
From there, Jesus goes on to help explain simple ways people fail obedience to the law, clarifying how easy it is to break. This must have been a scary time for his audience. (Thankfully, in Chapters 6 and 7 he provides examples of things we can do to help) Jesus was making it clear that God's standards are for obedience to the law without compromise. People must have been reminded not to claim too much righteousness on their own behalf. Jesus "fulfilled the law" with this interpretation.There must be perfect obedience, and that is not easy to do.
In short, Jesus sets his audience up to later understand the value of his sacrifice - his perfect obedience was the only possible way his blood could be a worthy sacrifice in our place! (sweet, these thoughts tie in with what Todd Agnew was talking about last night)