the difference between abolishing and fulfilling

Matthew 5:17-20

This is a tough passage for me to figure out. First I have to remember that Matthew is writing to Jewish audience what Jesus said to a Jewish audience. So I have to consider a) what Matthew's purpose is for including this passage and b) what Jesus' purpose was in saying it in the first place. I think that Matthew includes it because the Jewish audience would have remembered the accusations against Jesus: that he broke and dishonored the Law. Matthew is using the words of Jesus himself to tell them that he didn't dishonor the Law but, just the opposite, brought full honor and authority back to the Law. Jesus likely said these words for some of the same purposes but also to remind the people that they had been living according to human tradition and ideas about the Law and hadn't really been living to the standard of the Law's true intent.
The key words in this passage are: "abolish" as compared to "fulfill", "smallest letter", "least stroke of a pen". "Least" is a word that gets repeated a few times: "least stroke of a pen", "least of these commands" and "least in the kingdom of heaven". Jesus does seem to indicate that there is a hierarchy of laws and that there will be a hierarchy in the kingdom of heaven. The kingdom of heaven is a theme in this passage (in fact in the whole sermon on the mount).
The difficult thing for me is figuring out what Jesus means. What he seems to say is that the Law must be fully obeyed (even to the smallest commandment). However, looking at the life of Jesus, we see that he broke commands about working on the Sabbath. Even as I say that, I wonder if Jesus broke established tradition surrounding the Law and didn't break the Law itself. Certainly Paul had no issues with "breaking" parts of the Law - specifically baptism, etc. - and certainly Jesus cannot expect us to keep the parts of the Law surrounding the sacrificial system of the temple because a) there is no temple right now and b) the teaching of Scripture is pretty clear that the sacrificial system was a temporary sign that pointed to the ultimate and eternal sacrifice that Jesus made of himself on the cross.
In the context of the whole Sermon, teaching and life of Jesus and Scripture, it is likely that Jesus is teaching against the hypocritical tradition that surrounds the Law that allows for loopholes and justification and misses the whole point of the Law (for example, saying that you can spit on a rock on the Sabbath but can't spit on dirt because that would make clay which equals work probably means that we've missed the point of the Sabbath). The question still remains, what does this mean for me? Do I have to obey even the smallest command and teach others to do the same? That would certainly seem like the "plain meaning" of Jesus' teaching in this paragraph but this doesn't seem to match the context and the rest of his life and teaching. Perhaps Jesus is reminding us that there is something more than the letter of the Law that needs to be considered. We have to obey the full meaning or intent of the Law. So we as followers of Jesus under the new covenant do not have to follow all the Laws about ceremonies and sacrifices and cloth blends and kosher meats but we do have to do everything in Christ's power to love God with all we have and are and love our neighbour as ourselves. Jesus will teach in the following sections that I must not only live up to the letter of the Law when it comes to murder and adultery and divorce but that I must represent the character of God in my interactions with all humanity in terms of purity, love and dignity.
This truly is a righteousness that surpasses the oral tradition of the Pharisees and teachers of the law. My only hope is that the righteousness of Christ will be substituted for my unrighteousness because I, in myself, cannot live up to that standard. Maybe that's the point.