The former Jewish priests were not adequate, so a new one like Melchizedek had to come.

Hebrews 7:11-19

11 God gave his laws to his people at the same time he gave regulations about the priests. So, if what the priests who were descended from Levi did could have provided a way for God to completely forgive people for disobeying those laws, certainly no other priest like Melchizedek would have been necessary. [RHQ] Instead, priests who were descended from Aaron, Levi’s descendant, would have been adequate. 12 But we know they were not adequate, because a new type of priest like Melchizedek has come. And since God has appointed a new type of priest, he also had to change the regulations concerning how priests were appointed {he appointed priests}. 13 Jesus, the one about whom I am saying these things, is a descendant of someone else, not a descendant of Levi. None of the men from whom Jesus descended ever served as priests [MTY]. 14 We know that since it is obvious that it is from the tribe of Judah that our Lord was descended. Moses never said that any of Judah’s descendants would become priests. 15 Furthermore, we know that the priests who were descended from Levi were inadequate, since it is even more obvious that another priest has appeared who is like Melchizedek. 16 Jesus became a priest, but not because he fulfilled what God’s law required about being a descendant of Levi. Instead, he has the kind of power that came from a life that nothing can destroy (OR, enabled him to live again after he was killed). 17 We know this since God confirmed it in the Scripture passage in which he said to his Son,

You (sg) are a priest eternally just like Melchizedek was a priest.

18 On the one hand, God canceled what he commanded previously concerning the priests because it failed in every way to enable anyone to become all that God intended. 19 Remember that no one was able to become all that God intended by obeying the laws that God gave Moses. On the other hand, God caused that we could confidently expect better things than we could expect by obeying God’s laws. He did that by his establishing Christ as priest. Now by means of Christ sacrificing himself for us we can come near to God.