1 Chronicles 24:3

3 David, with the help of Zadok from Eleazar's family and Ahimelech from Ithamar's family, divided them according to their appointed duties.

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 The divisions of the Aaronites: Aaron's family: Nadab, Abihu, Eleazar, and Ithamar.

2 Nadab and Abihu died before their father did, without having sons, and so Eleazar and Ithamar served as priests.

3 David, with the help of Zadok from Eleazar's family and Ahimelech from Ithamar's family, divided them according to their appointed duties.

4 Since Eleazar's family was found to have more male heads than Ithamar's family, they divided them so that Eleazar's family had sixteen household heads and Ithamar's family had eight.

5 They divided both groups by lots because there were holy leaders, even outstanding leaders, among both Eleazar's and Ithamar's descendants.