execute the priest's office

Boyd’s Bible Dictionary:

(presbyter, elder). Representative of man in things appertaining to God. Assistants of Moses as mediator (Ex. 24:55And he sent young men of the children of Israel, which offered burnt offerings, and sacrificed peace offerings of oxen unto the Lord. (Exodus 24:5)). Function of priesthood conferred on Levites (Ex. 28). Priests divided into regular courses (1 Chron. 24:1-191Now these are the divisions of the sons of Aaron. The sons of Aaron; Nadab, and Abihu, Eleazar, and Ithamar. 2But Nadab and Abihu died before their father, and had no children: therefore Eleazar and Ithamar executed the priest's office. 3And David distributed them, both Zadok of the sons of Eleazar, and Ahimelech of the sons of Ithamar, according to their offices in their service. 4And there were more chief men found of the sons of Eleazar than of the sons of Ithamar; and thus were they divided. Among the sons of Eleazar there were sixteen chief men of the house of their fathers, and eight among the sons of Ithamar according to the house of their fathers. 5Thus were they divided by lot, one sort with another; for the governors of the sanctuary, and governors of the house of God, were of the sons of Eleazar, and of the sons of Ithamar. 6And Shemaiah the son of Nethaneel the scribe, one of the Levites, wrote them before the king, and the princes, and Zadok the priest, and Ahimelech the son of Abiathar, and before the chief of the fathers of the priests and Levites: one principal household being taken for Eleazar, and one taken for Ithamar. 7Now the first lot came forth to Jehoiarib, the second to Jedaiah, 8The third to Harim, the fourth to Seorim, 9The fifth to Malchijah, the sixth to Mijamin, 10The seventh to Hakkoz, the eighth to Abijah, 11The ninth to Jeshua, the tenth to Shecaniah, 12The eleventh to Eliashib, the twelfth to Jakim, 13The thirteenth to Huppah, the fourteenth to Jeshebeab, 14The fifteenth to Bilgah, the sixteenth to Immer, 15The seventeenth to Hezir, the eighteenth to Aphses, 16The nineteenth to Pethahiah, the twentieth to Jehezekel, 17The one and twentieth to Jachin, the two and twentieth to Gamul, 18The three and twentieth to Delaiah, the four and twentieth to Maaziah. 19These were the orderings of them in their service to come into the house of the Lord, according to their manner, under Aaron their father, as the Lord God of Israel had commanded him. (1 Chronicles 24:1‑19); 2 Chron. 23:88So the Levites and all Judah did according to all things that Jehoiada the priest had commanded, and took every man his men that were to come in on the sabbath, with them that were to go out on the sabbath: for Jehoiada the priest dismissed not the courses. (2 Chronicles 23:8); Luke 1:55There was in the days of Herod, the king of Judea, a certain priest named Zacharias, of the course of Abia: and his wife was of the daughters of Aaron, and her name was Elisabeth. (Luke 1:5)).

Concise Bible Dictionary:

It is remarkable that the first priest spoken of in scripture is Melchizedek: he is said to be “priest of the most high God.” Nothing is said of his offering sacrifices, but he brought forth bread and wine, and blessed Abraham (Gen. 14:18-1918And Melchizedek king of Salem brought forth bread and wine: and he was the priest of the most high God. 19And he blessed him, and said, Blessed be Abram of the most high God, possessor of heaven and earth: (Genesis 14:18‑19)). He is a type of Christ, who is constituted a “priest after the order of Melchizedek,” and who will come forth to bless His people in the future. See MELCHIZEDEK.
Before the institution of the Levitical priesthood, Israel had been redeemed out of Egypt. The object of priesthood was not therefore to bring them into redemption, but to maintain their position based on redemption before God. At first it was said that they should all be priests (Ex. 19:66And ye shall be unto me a kingdom of priests, and an holy nation. These are the words which thou shalt speak unto the children of Israel. (Exodus 19:6)), but law afterward came in, and the service of priesthood was very definitely confined to the house of Aaron. The names of the twelve tribes were engraved on the breastplate and on the plates on the priest’s shoulders: whenever he went in to the presence of God, the people were thus represented. So Christ is the great High Priest at the right hand of God, not for the world, but for His saints: “We have such an high priest, who is set on the right hand of the throne of the Majesty in the heavens” (Heb. 8:11Now of the things which we have spoken this is the sum: We have such an high priest, who is set on the right hand of the throne of the Majesty in the heavens; (Hebrews 8:1)). He represents His saints there, and in virtue of His presence there, and of His experience here, He is able to sympathize with them in trial and to succor them in temptation.

Strong’s Dictionary of Greek Words:

Number:
2407 (find all occurrences in KJV Bible)
Greek:
ἱερατεύω
Transliteration:
hierateuo
Phonic:
hee-er-at-yoo’-o
Meaning:
prolongation from 2409; to be a priest, i.e. perform his functions
KJV Usage:
execute the priest's office