The Commandments promise, "This do and live." Presumably this is about living now. The Beatitudes are about happiness now and living forever.
It has always amazed me that as Christians we are more familiar with the particulars of the law than we are with the beatitudes. I really think that the Lord was consciously using the Beatitudes to transition from the Law to spiritual, eternal reality. The Law comes with a certain curse. In the upside-down Kingdom of our Lord the Beatitudes all come with blessing - and all without diminishing the law. In fact, they are the way to fulfill the law.
If you sit down and read the Sermon on the Mount you can't help but believe the Lord was very consciously stepping up from the law. He referred to if often (in fact He referenced each Commandment except the Sabbath) but warned that if our righteousness does not exceed that of the teachers of the law we will not see the Kingdom of Heaven. That is because the Law doesn't change us on the inside. The Sermon on the Mount takes us to the spirit of the commandments. It raises the bar and clinches the absolute impossibility of compliance in our own effort. May God help us graduate from being pretend "Doers" to a genuine state of transformed Beings.
