Melchizedek was the king of Salem. He was the priest of God Most High. He met Abraham, who was returning from winning a battle over some kings. Melchizedek blessed him.
Melchizedek has no father or mother. He has no family line. His days have no beginning. His life has no end. He remains a priest forever, just like the Son of God.
Now the law lays down a rule for the sons of Levi who become priests. They must collect a tenth from the people. They must collect it even from those who belong to the family line of Abraham.
Suppose the Levites who were priests could have made people perfect. The law was given to the people so they could become perfect through the priests. Then why was there still a need for another priest to come? And why did he need to be like Melchizedek? Why wasn't he from Aaron's family line?
He has not become a priest because of a rule about his family line. He has become a priest because of his powerful life. His life can never be destroyed.
But Jesus became a priest with an oath. God said to him, "The Lord has taken an oath and made a promise. He will not change his mind. He has said, 'You are a priest forever.' " --(Psalm 110:4)
A high priest like that meets our need. He is holy, pure and without blame. He isn't like other people. He does not sin. He is lifted high above the heavens.
He isn't like the other high priests. They need to offer sacrifices day after day. First they bring offerings for their own sins. Then they do it for the sins of the people. But Jesus gave one sacrifice for the sins of the people. He gave it once and for all time. He did it by offering himself.