So if the priesthood of Levi, on which the law was based, could have achieved the perfection God intended, why did God need to establish a different priesthood, with a priest in the order of Melchizedek instead of the order of Levi and Aaron?
And if the priesthood is changed, the law must also be changed to permit it. For the priest we are talking about belongs to a different tribe, whose members have never served at the altar as priests. What I mean is, our Lord came from the tribe of Judah, and Moses never mentioned priests coming from that tribe.
This change has been made very clear since a different priest, who is like Melchizedek, has appeared. Jesus became a priest, not by meeting the physical requirement of belonging to the tribe of Levi, but by the power of a life that cannot be destroyed. And the psalmist pointed this out when he prophesied,
“You are a priest forever in the order of Melchizedek.”
Yes, the old requirement about the priesthood was set aside because it was weak and useless. For the law never made anything perfect. But now we have confidence in a better hope, through which we draw near to God.
This new system was established with a solemn oath. Aaron’s descendants became priests without such an oath, but there was an oath regarding Jesus. For God said to him,
“The LORD has taken an oath and will not break his vow:
‘You are a priest forever.’”
Because of this oath, Jesus is the one who guarantees this better covenant with God.