Nevertheless, Jesus does change the law. For example in Deuteronomy 19:21 it says: "Do not look on such a man with pity. Life for life, eye for eye, tooth for tooth, hand for hand, and foot for foot! " NAB. See, Leviticus 24:19-21. But Jesus says in Matt 5:38-39: ""You have heard that it was said, 'An eye for an eye and a tooth for a tooth.' But I say to you, offer no resistance to one who is evil. When someone strikes you on (your) right cheek, turn the other one to him as well." NAB.
Jesus made other changes to the accepted understanding of what God had commanded. The dietary laws required a Jew to abstain from certain foods or become unclean, i.e.. out of harmony with God. See Lividicus 11. But Jesus declared food clean.
In Mark 7:1-8 Jesus disallows the ceremonial washing the Pharisees taught was required. He did this despite Lev. 10:10 "You must be able to distinguish between what is sacred and what is profane, between what is clean and what is unclean..." NAB.
Because each of Jesus' statements are without error, their true meaning must be non-contradictory, that is each apparent change in the Law of God must not contradict his statement that the law cannot change. Thus the Catechism of the Catholic Church says in section 1967 "The Law of the Gospel "fulfills," refines, surpasses, and leads the Old Law to its perfection..."
Jesus himself accuses the Pharisees of changing or even negating God's genuine law. Mark 7:13: "You nullify the word of God in favor of your tradition that you have handed on." NAB. Therefore, what the religious leaders were teaching did not conform to what God's law actually was. How could he know this, or make this assertion? By being God's Prophet, Messiah, Son, and being God Himself, the second person of the Trinity.
We are bound to the old Jewish Law of Moses only to the extent it has been confirmed, ratified, and restated by Christ.