The office of priest, as defined and chosen by God was confined to the male descendants of Aaron (Moses’ brother) of the tribe of Levi. After the rebellion of Korah, Dathan, Abiram and On, detailed in Numbers 16-17, confirmation was given of God’s earlier choice of Aaron and Levi, where one rod for each tribe were laid up in the tabernacle and Aaron’s rod produced almond blossom and fruit (Numbers 17). The following statement is then made:-
Numbers 18:1-7 And the LORD said unto Aaron, Thou and thy sons and thy father’s house with thee shall bear the iniquity of the sanctuary: and thou and thy sons with thee shall bear the iniquity of your priesthood. And thy brethren also of the tribe of Levi, the tribe of thy father, bring thou with thee, that they may be joined unto thee, and minister unto thee: but thou and thy sons with thee shall minister before the tabernacle of witness. And they shall keep thy charge, and the charge of all the tabernacle: only they shall not come nigh the vessels of the sanctuary and the altar, that neither they, nor ye also, die. And they shall be joined unto thee, and keep the charge of the tabernacle of the congregation, for all the service of the tabernacle: and a stranger shall not come nigh unto you. And ye shall keep the charge of the sanctuary, and the charge of the altar: that there be no wrath any more upon the children of Israel. And I, behold, I have taken your brethren the Levites from among the children of Israel: to you they are given as a gift for the LORD, to do the service of the tabernacle of the congregation. Therefore thou and thy sons with thee shall keep your priest’s office for every thing of the altar, and within the vail; and ye shall serve: I have given your priest’s office unto you as a service of gift: and the stranger that cometh nigh shall be put to death.
2 Chronicles 26:16-21 describes an incident where Uzziah, king of Judah, sought to offer incense himself in the temple, and Azariah the High Priest withstood him. Uzziah was smitten with leprosy because of this attempted act.
Ezra 2:61-62 details a genealogical dispute over rights to inclusion in the priesthood.
Aaron was chosen as the first High Priest, a lifetime office which was inherited by the oldest male heir from generation to generation. The supporting priests were Aaron’s sons, Nadab, Abihu, Eleazar and Ithamar, however Nadab and Abihu were slain because they offered strange fire at the tabernacle inauguration, thus the duties were left to Eleazar and Ithamar and their sons. Eleazar succeeded his father Aaron at his death who was later succeeded by his firstborn son Phinehas.
The rest of the males from the tribe of Levi had responsibility for support activities such as transport of the tabernacle (Numbers 4, Numbers 8:19-26). Later King David and Solomon established courses of; 1 month in 24 for the priests and other Levitical temple support duties (1 Chronicles 23:6, 2 Chronicles 8:14).
When settled in the land of Israel, most of the tribes had a contiguous inheritance, however, Levi’s inheritance was divided as specific named cities within each of the other tribes. Defined portions of the people’s offerings, effectively formed the priesthoods stipend, acknowledging the crucial role they played on Israel’s behalf.
In addition to the priest’s ceremonial and ecclesiastical role, they also had supportive responsibilities in administration of the civil law. For example they were to be a source of knowledge:- Malachai 2:7 the priest’s lips should keep knowledge, and they should seek the law at his mouth: for he is the messenger of the LORD of hosts. Examples of other duties included diagnosis of leprosy (Leviticus 13-14), and decisions on actions required when a murderer could not be found (Deuteronomy 21:1-9) etc.
Specific garments were required for the priests for their duties in the tabernacle. The High Priest’s garments are described in detail in Exodus 28, Exodus 28:4 a breastplate, and an ephod, and a robe, and a broidered coat, a mitre, and a girdle: and they shall make holy garments for Aaron. The usage of priest’s clothing is mandated in Exodus 28:43 they shall be upon Aaron, and upon his sons, when they
come in unto the tabernacle of the congregation, or when they come near unto the altar to minister in the holy place; that they bear not iniquity, and die: it shall be a statute for ever unto him and his seed after him. The breastplate, contained 12 precious stones, to represent the 12 tribes of Israel on whose behalf the High Priest was ministering. Exodus 29, Exodus 40 and Leviticus 8-9 give details of the consecration ceremony of Aaron and his sons as priests, including washing with water for purification, animal sacrifices and anointing.