Righteousness...

I read Matthew 5 today. Usually I'm encouraged and inspired by the beattitudes... mainly because I don't like to read far enough to get to the part about hate, lust and loving my enemies. However today I got stuck between the two.
Matthew 5:17-20 says,
"17"Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them but to fulfill them. 18I tell you the truth, until heaven and earth disappear, not the smallest letter, not the least stroke of a pen, will by any means disappear from the Law until everything is accomplished. 19Anyone who breaks one of the least of these commandments and teaches others to do the same will be called least in the kingdom of heaven, but whoever practices and teaches these commands will be called great in the kingdom of heaven. 20For I tell you that unless your righteousness surpasses that of the Pharisees and the teachers of the law, you will certainly not enter the kingdom of heaven."
Make no mistake, God is not done with the OT law and it's expectations. I was always taught that the new covenant replaced the old one... that the law was for those under the law and we are under grace. No quite so. So I was challenged... which am I? Great or least in the kingdom? I do try to obey and I teach a lot. (To be honest, looking back, I've taught a lot of bad theology. And it's funny how arrogant I can be when I teach the Bible. Afterall, it is the infallible, divinely inspired Word of God - how could I (it) be wrong?)
At any rate, I've been more and more challenged lately to go back and really obey the Old Testament. It's pretty tough! But I find that if I focus on the OT also, it's a whole lot easier to obey the Jesus stuff of the NT... and vice-versa. Strange, almost as if God had something in mind?..?.. Huh.