Jesus didn't say this, so it is not the teaching of Jesus....you are confusing the teachings of Jesus with the teachings of Paul.
Jesus said: Do not think that I have come to abolish the Law or the Prophets. Where did Jesus change His mind and then say He came to change Mosaic Law??
Who is lying? Jesus or Paul??
I'll just pop in the passage from the sermon on the mount for reference:
Matthew 5
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.
18 For 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.
19 Therefore 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.
20 For I tell you, unless your righteousness exceeds that of the scribes and Pharisees, you will never enter the kingdom of heaven.
21 You have heard that it was said to those of old, 'You shall not murder; and whoever murders will be liable to judgment.'
22 But I say to you that everyone who is angry with his brother will be liable to judgment; whoever insults his brother will be liable to the council; and whoever says, 'You fool!' will be liable to the hell of fire.
23 So if you are offering your gift at the altar and there remember that your brother has something against you,
24 leave your gift there before the altar and go. First be reconciled to your brother, and then come and offer your gift.
25 Come to terms quickly with your accuser while you are going with him to court, lest your accuser hand you over to the judge, and the judge to the guard, and you be put in prison.
26Truly, I say to you, you will never get out until you have paid the last penny.
27 You have heard that it was said, 'You shall not commit adultery.'
28 But I say to you that everyone who looks at a woman with lustful intent has already committed adultery with her in his heart.
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What he was saying is that the scribes and Pharisees were exaggerating every tenet of law until it became a burden on the people and ritualistic behaviour became more important than the underlying principles.
This is more obviously stated in Matthew 23:
23 Woe to you, scribes and Pharisees, hypocrites! For you tithe mint and dill and cumin, and have neglected the weightier matters of the law: justice and mercy and faithfulness. These you ought to have done, without neglecting the others.
24 You blind guides, straining out a gnat and swallowing a camel!
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Jesus did not come to stop people from acting in the spirit of the Mosaic law, he was more concerned with the underlying principles of how man should treat man rather than the minute details of each law (as the priests were doing).
21 You have heard that it was said to those of old, 'You shall not murder; and whoever murders will be liable to judgment.'
22 But I say to you that everyone who is angry with his brother will be liable to judgment;
He is saying, you're missing the point, you should look beyond the letter of the law, you should always aim to behave with benevolence regardless of the specific situation, not be bogged down by a checklist of dos and don'ts.
He is not abolishing the law, but rather the dogmatic, ritualistic way of applying the law that was getting in the way of it's genuine application.
18 For 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.
The early Jews made sacrifices to god in order to repent for their transgressions against the law. When Jesus said he would fulfil the law it meant he would sacrifice himself and that would release all mankind from sin and from the literal Mosaic law.