Another common misconception about the Law of Moses is that it contains a complete list of all sins. This is just not true.
God gave the law revealed to Moses to provide a way for people to live in harmony. It was not intended to be a list of all sins. Pride is not mentioned in the Ten Commandments. Neither is presumption or gluttony. We should not be surprised at these omissions, because this is not the purpose of the law.
Moses understood this. He was the most humble man on the earth, even though humility is not one of the Ten Commandments. He was humble because he loved God, not because of the law. He understood that the law was not given to define sin, but to provide a way for people to live in peace.
Jesus corrected this error in the Sermon on the Mount, by giving a true standard of righteousness. He then explained that keeping the law was not sufficient for a holy life. There are plenty of people who have never committed adultery, murdered someone, stolen from their neighbour or perjured themselves before a court, but that does not make them holy. Jesus explained that anger and lust are sins, even though they are not forbidden by the law.
Our righteousness must surpass the standard required by the law (Matt 5:20).
Be perfect, therefore, as your heavenly Father is perfect (Matt 5:48).
Keeping the law makes us peaceful citizens, but it does not make us holy. God’s holiness requires a much higher standard than the law.
Some Christians assume that Jesus was changing the law and setting a higher standard. This is not correct. He confirmed the law.
Do not think that I have come to abolish the Law or the Prophets; I havenot come to abolish them but to fulfill them. I tell you the truth, until heavenand 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 (Matt5:17-18).
Jesus was not changing the law. He was explaining the difference between the laws needed for the harmonious working of society and the standard of holiness of righteousness required by holiness. The law is sufficient for people to live in harmony, because that is its purpose. It is not our standard of holiness.