The Decalogue in the Torah which you call the OT law of sin and death, is rather the Law of grace and life. Have you ever read Psalm 119? Probably not. That's why. The Law of Jesus was exactly the Law in the Torah. If you want an evidence for what I am saying, read Mat. 5:17-19 and Luke 16:29-31. Jesus himself warned us all to listen to "Moses" aka the Law to achieve salvation. Now, this change you are talking about of the Law and the Priesthood, is called the Pauline policy of Replacement Theology which is the vandalism of the Faith of Jesus which was Judaism with the faith of Paul which was the Church he founded aka Christianity. (Acts 11:26)
I said
Not so. The old testament law of an eye for an eye. The new testament is turn the other cheek. There is no way anyone can do them both at the same time.
Matt 5:29-44
29 "If your right eye causes you to sin, pluck it out and cast it from you; for it is more profitable for you that one of your members perish, than for your whole body to be cast into hell.
30 "And if your right hand causes you to sin, cut it off and cast it from you; for it is more profitable for you that one of your members perish, than for your whole body to be cast into hell.
31 "Furthermore it has been said, 'Whoever divorces his wife, let him give her a certificate of divorce.'
32 "But I say to you that whoever divorces his wife for any reason except sexual immorality causes her to commit adultery; and whoever marries a woman who is divorced commits adultery.
33 "Again you have heard that it was said to those of old, 'You shall not swear falsely, but shall perform your oaths to the Lord.'
34 "But I say to you, do not swear at all: neither by heaven, for it is God's throne;
35 "nor by the earth, for it is His footstool; nor by Jerusalem, for it is the city of the great King.
36 "Nor shall you swear by your head, because you cannot make one hair white or black.
37 "But let your 'Yes' be 'Yes,' and your 'No,' 'No.' For whatever is more than these is from the evil one.
38 "You have heard that it was said, 'An eye for an eye and a tooth for a tooth.'
39 "But I tell you not to resist an evil person. But whoever slaps you on your right cheek, turn the other to him also.
40 "If anyone wants to sue you and take away your tunic, let him have your cloak also.
41 "And whoever compels you to go one mile, go with him two.
42 "Give to him who asks you, and from him who wants to borrow from you do not turn away.
43 "You have heard that it was said, 'You shall love your neighbor and hate your enemy.'
44 "But I say to you, love your enemies, bless those who curse you, do good to those who hate you, and pray for those who spitefully use you and persecute you,
(NKJ)