Exodus 20:13 says "Thou shalt not kill." So that is Mosaic law but Jesus gives us the higher law here: "Ye have heard that it was said of them of old time, Thou shalt not kill; and whosoever shall kill shall be in danger of the judgment:
22 But I say unto you, That whosoever is angry with his brother without a cause shall be in danger of the judgment: and whosoever shall say to his brother, Raca, shall be in danger of the council: but whosoever shall say, Thou fool, shall be in danger of hell fire.
23 Therefore if thou bring thy gift to the altar, and there rememberest that thy brother hath ought against thee;
24 Leave there thy gift before the altar, and go thy way; first be reconciled to thy brother, and then come and offer thy gift.
25 Agree with thine adversary quickly, whiles thou art in the way with him; lest at any time the adversary deliver thee to the judge, and the judge deliver thee to the officer, and thou be cast into prison.
Matthew 5:21-25
So not killing fulfills the law but making amends and quelling our anger is living the higher law. Which is why Jesus taught us to love not only those who are good to us but to love our enemies as well.
Exodus 20:14 says "Thou shalt not commit adultery." Being faithful upholds the Mosaic law but again Jesus gives us the higher law here:
27 Ye have heard that it was said by them of old time, Thou shalt not commit adultery:
28 But I say unto you, That whosoever looketh on a woman to lust after her hath committed adultery with her already in his heart. Matthew 5:27-28
What set Jesus apart from Jewish teachers and Rabbis before and after Him is that while everyone else nit picked the law to prescribe the perfect mode of living up to the law in every possible situation.
And those admonishments were always about doing the least. At the least take no more than was taken from you. Where as Jesus said if someone takes your shirt give them your cloak also.
Jesus taught us to do the most rather than the least. He admonished us to be the best rather than merely being good enough not to go to Hell.
Lamech he was a wicked character and arguably the most wicked but certainly the most vengeful man in scripture because of how severe his vengeance was.
24 If Cain shall be avenged sevenfold, truly Lamech seventy and sevenfold. Genesis 4:24
It's important to understand that 77 was a symbol for infinity so to say he shall be avenged 77 times is to say he will inflict eternal punishment for limited sin.
Even if it were legal to be avenged for infinity Jesus again gives us the higher law: 21 Then came Peter to him, and said, Lord, how oft shall my brother sin against me, and I forgive him? till seven times?
22 Jesus saith unto him, I say not unto thee, Until seven times: but, Until seventy times seven. Matthew 18:21-22
Jesus teaches Peter and ultimately us that there should not be any exceptions or limits to our forgiveness and teaches also that if we do judge we will be judged by the same standard with which we judged.
Jesus did not contradict Mosaic law, He gave us a higher law. He gave us principles to guide our lives by so that we wouldn't need legalistic code books to tell us what the right thing to do or say in any given situation is.
We can live by the commandments and maybe get into Heaven or we can live the higher law and build up the Kingdom of God.
When Jesus tells us to forgive 77 times, to me He is saying why be the average or why be the worst character in scripture when you could be the best?
Jesus taught us the higher law because He believes that each of us can live up to that higher law. We would not have been taught a law if we were not capable of following it. We can be the best version of ourselves and to be that frees us ultimately.
The foundation on which all the prophets and laws are founded on is a love of God and all His children. Jesus taught us to be better than average, He taught us to be great. But Jesus went beyond the doing, He stressed the being.
