1 Chronicles 24:3

3 And David distributed them, both Zadok of the sons of Eleazar, and Ahimelech of the sons of Ithamar, according to their office in their service.

1 Chronicles 24:3 Meaning and Commentary

1 Chronicles 24:3

And David distributed them
The posterities of Eleazar and Ithamar into certain classes or courses:

both Zadok of the sons of Eleazar, and Ahimelech of the sons of
Ithamar;
these were the two principal men of the respective families, the one was high priest, and the other "sagan" or deputy; or they both officiated as high priests alternately, until the one was removed in Solomon's time, and the other established alone. And now their brethren the priests, who were under each of these, are the persons David divided into classes:

according to their offices in their service:
to perform their office as priests in the service of the temple in their turns.

1 Chronicles 24:3 In-Context

1 And the divisions of the sons of Aaron: the sons of Aaron, Nadab and Abihu, Eleazar and Ithamar.

2 And Nadab and Abihu died before their father, and had no children; and Eleazar and Ithamar exercised the priesthood.

3 And David distributed them, both Zadok of the sons of Eleazar, and Ahimelech of the sons of Ithamar, according to their office in their service.

4 And there were more head-men found of the sons of Eleazar than of the sons of Ithamar, and [thus] were they divided: of the sons of Eleazar there were sixteen heads of fathers' houses, and eight of the sons of Ithamar according to their fathers' houses.

5 And they were divided by lot, one with another; for the princes of the sanctuary and the princes of God were of the sons of Eleazar and of the sons of Ithamar.