Love of neighbor was certainly a commandment of the Old Law. Sometimes we might imagine that Jesus’ commandment of love was something revolutionary. What is revolutionary – at His time – is the shift of emphasis. We live thousands of years later and are completely unacquainted with the daily practice of the Old Covenant. We consider the old and external practices to be the unimportant details of religious observance. That is our modern perspective, so when we hear Jesus telling us not to neglect the least of the commandments, we suppose He is referring to the minute points of external observance. In fact, Jesus is speaking to the world-view of his listeners, who are used to considering the commandments concerning love as “least.”
Wouldn’t it be horribly backwards if we started making the detailed points of religious observance more important than the New Commandment of Love because we thought that’s what Jesus meant by not neglecting the least of the commandments? We would go back to being Pharisees! Remember how Jesus praised the scribe who remarked “Right, Teacher; You have truly stated that […] to love Him [the Lord] with all the heart and with all the understanding and with all the strength, and to love one’s neighbor as oneself, is much more than all burnt offerings and sacrifices.” (Mark 12:30) The real difficulty of being religious and Christian is to not neglect practicing the “least” commandment: the commandment of love.
He therefore rebukes the Pharisees, who showed contempt for God’s commandments and set up their own traditions, for their teaching among the people is of no value if they destroy even a small part of what is in the law. We can understand this in another sense, namely, that a teacher’s learning, even if tainted by a small sin, demotes him from the highest place. It does not profit him to teach a righteousness that he undermines by the slightest fault. The Beatitude is perfected if what you teach with your words you practice with your works.1
Note how Jesus also in this passage commends the old law. He does so by comparing it with the new, a comparison that implies that it is of the same family, so to speak. More or less, it does share many family resemblances. He does not find fault with the old law but in fact makes it more strict. Had it been evil, Jesus would not have accentuated it. Instead, he would have discarded it.
If the law is so commendable, how is it not adequate to bring us into the kingdom? After the coming of Christ we are favored with a greater strength than law as such. Those who are adopted as children are bound to strive for greater things.2