Old Testament moral law's are Still in effect today, and are to be obeyed!
If we want to be "great" then we are to "practice and teach this". If we want to be "Least" then break one of the least of the commandments and teach others to do the same. I do not know what it means to teach. But with so much riding on this we should put some effort into trying to figure out what Jesus is teaching us here.
If people say we do not have to follow the law, then they are saying we do not have to love God and we do not have to love our neighbor as ourself. Sometimes I wonder between God, our neighbor and our-self. The most difficult maybe to love our-self.