'Priesthood' in the Bible

it fell to his lot--according to the custom of the priesthood--to go into the Sanctuary of the Lord and burn the incense;

And those of the descendants of Levi who receive the priesthood are authorized by the Law to take tithes from the people, that is, from their brethren, though these have sprung from Abraham.

Now if the crowning blessing was attainable by means of the Levitical priesthood--for as resting on this foundation the people received the Law, to which they are still subject-- what further need was there for a Priest of a different kind to be raised up belonging to the order of Melchizedek instead of being said to belong to the order of Aaron?

For when the priesthood changes, a change of Law also of necessity takes place.

but He, because He continues for ever, has a priesthood which does not pass to any successor.

And be yourselves also like living stones that are being built up into a spiritual house, to become a holy priesthood to offer spiritual sacrifices acceptable to God through Jesus Christ.

But you are a chosen race, a priesthood of kingly lineage, a holy nation, a people belonging specially to God, that you may make known the perfections of Him who called you out of darkness into His marvellous light.