'Priesthood' in the Bible

he was chosen by lot, according to the custom of the priesthood, to enter the holy place of the Lord and burn incense.

So if perfection had in fact been possible through the Levitical priesthood -- for on that basis the people received the law -- what further need would there have been for another priest to arise, said to be in the order of Melchizedek and not in Aaron's order?

For when the priesthood changes, a change in the law must come as well.

but he holds his priesthood permanently since he lives forever.

you yourselves, as living stones, are built up as a spiritual house to be a holy priesthood and to offer spiritual sacrifices that are acceptable to God through Jesus Christ.

But you are a chosen race, a royal priesthood, a holy nation, a people of his own, so that you may proclaim the virtues of the one who called you out of darkness into his marvelous light.