The Gospel of Matthew contains most of the proofs that the Law of Moses was just as obligatory for Christians as it was for the Hebrews that Moses gave it to.  Nobody wants to think about that for the Law is very threatening and hateful and for every nice statement there are hundreds of cruel and bloody ones.
In Matthew 5, Jesus says that he has come to fulfil the Law and the Prophets, the two major sections in the Old Testament, not to prohibit them. Then he says that not an iota shall pass from them. He is promising to preserve the perfectly. Then he asserts that it is a sin to break or abolish even one of their commandments.
The word for fulfil in the original text is the Greek word pleroo. Pleroo appears in Matthew 13:48 where a net is pleroo or filled up with fish. Pleroo means that instead of changing or cancelling the Law he would fill it up until it could hold no more which is the same as saying he will expand the Law and make it complete (page 16, The World Ahead, November December 1998, Vol 6, Issue 6).
He is saying that he will not do away with the rules in the Law. He said some stuff after that many take to be in contradiction of the Law. But he said he would not do away. So what comes after must not be interpreted so as to be supposed to be in contradiction to the Law.
Some have said that when Jesus said after he came to fulfil the Law that anybody who breaks the smallest of the commandments will be the lowest in the kingdom of Heaven he meant the commandments he gave later on. But when he was after speaking about the Law his listeners who were naïve and irreligious would certainly have assumed that the commandments had to be those of the Law. So, Jesus condemned people who broke the Law of Moses.
He did not simply mean, “I have not come to do away with the text of the Law but to fulfil it”. If he had he would have put the word text in in case his listeners who were ordinary people would misunderstand. The Law is not the text or it’s wording but is expressed in letters and words and in sentences. Jesus would not have talked as if he was expected to do away with the text and replace it for nobody expected anything so absurd.
“He did not actually say that it would be a sin for him to repeal the divine laws,” reply the theologians who want to use this as an excuse for denying my natural interpretation of what Jesus said. But he never said, “It is a sin for anybody except me to alter the commandments of the Law”. He meant that even he himself was excluded from the privilege of altering the Law.

Jesus said that our keeping the law or righteousness must be better than that of the scribes and Pharisees to enter the kingdom of Heaven (Matthew 5:20). We must obey the Jewish Law better than them. He did not like the Jews preferring the letter of the Law to the spirit of the Law. For example, the Jews read in the Law to love their neighbours. They interpreted this as meaning that they must love only those who live around them. But they did not understand that God meant that everybody is your neighbour. The misinterpretation is the letter of the Law and the real meaning is the spirit of the Law. If you take it overly literally it becomes the letter of the Law that you are obeying. Forget about the words and concentrate on the meaning.
Jesus said later that since the Law and the Prophets commanded that you do to others what you want them to do to you, you must obey (7:12). He categorically stated that the Law was still in force and said that this rule was a summary of the Law and the Prophets. A summary that drops out the parts is not a summary at all so Jesus was saying the Law should still be obeyed. If the summary rules out the brutal laws of the Law and the Prophets then it is not a summary.
The Church says that Jesus died for sinners to make up for sins. But it believes he didn’t need to die for all he had to do was obey God in our place and each act is full payment for our disobedience. The Church holds that since Jesus was God or supremely special to God only one act of obedience was needed to remove sin so Jesus made up for all sins simply by being conceived. To become man knowing that you have to give your life for sinners on the cross would be the same value as dying on the cross. After the atonement, Jesus told his disciples to obey everything the scribes and the Pharisees tell them but not to emulate their hypocrisy (Matthew 23:2,3). And their teachers preached that Jesus must be ready and willing to kill and give an eye for an eye for the Law says so.
Christ castigated the Jews for not obeying God’s word when it demanded that anybody who did not respect parents had to be put to death (Matthew 15). He told them they were setting aside the wishes of God which would not have been the case if this law had been cancelled for then it would not have been there to have been set aside.
On the strength of God’s own authority, Jesus commanded the love of God and of neighbour (Matthew 22). He said that to him these meant what the Law commanded for all it demands depends on these two principles. In other words, he wanted the Law to be observed in full for its nature was love.
The people were told by Jesus to obey the scribes and Pharisees because they preached the Torah. He denounced them as evil men so he would not have told them to do what they say when their ideas were only their own reasoning. “Observe and practice all they tell you; but do not do what they do, for they preach, but do not practice” (Matthew 23:3).
Jesus told a young Jewish man to keep the commandments if he wanted to enter Heaven (Matthew 19:17). Christians say that this is not a proof that the Law is still in force for he went on to say he should keep the moral rules forbidding stealing and adultery and so on or the ten commandments in other words. But Jesus mentioned only a few commandments and quoted them as some but not all examples so he would have meant the other laws in and out of the Ten Commandments too. He certainly did not mean the man to think that only a couple of rules were binding. When he was speaking to a Jew he would have been understood to have referred to the entire Law and he was preaching obedience to the Law during his ministry. And because he said commandments instead of Ten Commandments he must have meant the entire law. Remember too that the Ten Commandments were just a summary of the Law of Moses meaning that to approve them is to approve of all the other laws too. The first commandment, You shall have no God but me – or you shall put nothing else before me and will obey me, enjoins obedience to the Law of God, the whole Law. It is a part of the Law after all.
Jesus said we should treat others as we want them to treat us FOR this fulfils the Law of Moses and the Prophets (Matthew 7:12). He tells us we should like to be stoned to death if we deserve it. This line says it all.
The Law is still to be obeyed.