So let me break this down for all who are confused about this matter. The New Testament is the fulfillment of the Old Testament. Not just the prophesies about the coming of the messiah but the Law (note the uppercase "L") given to the people of ancient Israel as well. By fulfillment I mean that the requirements of the Law and prophesies were met. On what do I base my assertions you ask? Here you go, from the Sermon on the Mount recorded in Matthew 5 Jesus Christ himself declares:
17"Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them but to fulfill them. 18For truly, I say to you, until heaven and earth pass away, not an iota, not a dot, will pass from the Law until all is accomplished. 19Therefore whoever relaxes one of the least of these commandments and teaches others to do the same will be called least in the kingdom of heaven, but whoever does them and teaches them will be called great in the kingdom of heaven. 20For I tell you, unless your righteousness exceeds that of the scribes and Pharisees, you will never enter the kingdom of heaven.
These words are the opening salvo of a incredibly harsh critique of the way the Law had been perverted by the very ones who were tasked with upholding it. Time and time again Jesus clashed with the religious leaders of his day because he wasn't observing the Law the way they thought it was to be observed. To modern eyes some of the things they were fussing about seem childish and petty. I think that was part of Jesus' purpose in challenging them to show how petty and corrupt they were.
1At that time Jesus went through the grainfields on the Sabbath. His disciples were hungry, and they began to pluck heads of grain and to eat. 2But when the Pharisees saw it, they said to him, "Look, your disciples are doing what is not lawful to do on the Sabbath." 3He said to them, "Have you not read what David did when he was hungry, and those who were with him: 4how he entered the house of God and ate the bread of the Presence, which it was not lawful for him to eat nor for those who were with him, but only for the priests? 5Or have you not read in the Law how on the Sabbath the priests in the temple profane the Sabbath and are guiltless? 6I tell you, something greater than the temple is here. 7And if you had known what this means, 'I desire mercy, and not sacrifice,' you would not have condemned the guiltless. 8For the Son of Man is lord of the Sabbath."
1Again he entered the synagogue, and a man was there with a withered hand. 2And they watched Jesus,[a] to see whether he would heal him on the Sabbath, so that they might accuse him. 3And he said to the man with the withered hand, "Come here." 4And he said to them, "Is it lawful on the Sabbath to do good or to do harm, to save life or to kill?" But they were silent. 5And he looked around at them with anger, grieved at their hardness of heart, and said to the man, "Stretch out your hand." He stretched it out, and his hand was restored. 6The Pharisees went out and immediately held counsel with the Herodians against him, how to destroy him.
1Then Pharisees and scribes came to Jesus from Jerusalem and said, 2"Why do your disciples break the tradition of the elders? For they do not wash their hands when they eat." 3He answered them, "And why do you break the commandment of God for the sake of your tradition? 4For God commanded, 'Honor your father and your mother,' and, 'Whoever reviles father or mother must surely die.' 5But you say, 'If anyone tells his father or his mother, What you would have gained from me is given to God,[a] 6he need not honor his father.' So for the sake of your tradition you have made void the word[b] of God. 7You hypocrites! Well did Isaiah prophesy of you, when he said:
8"'This people honors me with their lips,
but their heart is far from me;
9in vain do they worship me,
teaching as doctrines the commandments of men.'"
The religious leaders of the time were always looking for ways to trip Jesus up so that they could have a gottcha moment where they could declare him to be in violation of the law. But Jesus always upheld the importance of the Law.
34But when the Pharisees heard that he had silenced the Sadducees, they gathered together. 35And one of them, a lawyer, asked him a question to test him. 36"Teacher, which is the great commandment in the Law?" 37And he said to him, "You shall love the Lord your God with all your heart and with all your soul and with all your mind. 38This is the great and first commandment. 39And a second is like it: You shall love your neighbor as yourself. 40On these two commandments depend all the Law and the Prophets."
The Old Testament is the foundation upon which the house of the New Testament is built. The strength of the Old Testament is that it shows us God's people trying to live by God's standards. It isn't always pretty but we do have the examples of Joseph (sold into slavery to rule Egypt), David (the shephard boy who became king), and Daniel (rising to power in exile and surviving the lion's den).