'Priesthood' in the Bible

it happened that he was chosen by lot, according to the custom of the priesthood, to enter the sanctuary of the Lord and burn incense.

And verily they that are of the sons of Levi, who receive the office of the priesthood, have a commandment to take tithes of the people according to the law, that is, of their brethren, though they come out of the loins of Abraham:

Furthermore, here [in the Levitical priesthood] tithes are received by men who are subject to death; but in that case [concerning Melchizedek], they are received by one of whom it is testified that he lives on [perpetually].

If therefore perfection were by the Levitical priesthood, (for under it the people received the law,) what further need was there that another priest should rise after the order of Melchisedec, and not be called after the order of Aaron?

For the priesthood being changed, there is made of necessity a change also of the law.

For it is evident that our Lord sprang out of Juda; of which tribe Moses spake nothing concerning priesthood.

But this man, because he continueth ever, hath an unchangeable priesthood.

Ye also, as lively stones, are built up a spiritual house, an holy priesthood, to offer up spiritual sacrifices, acceptable to God by Jesus Christ.

But ye are a chosen generation, a royal priesthood, an holy nation, a peculiar people; that ye should shew forth the praises of him who hath called you out of darkness into his marvellous light: