1 Chronicles 24:3

3 David, Eleazar's descendant Zadok, and Ithamar's descendant Ahimelech divided Aaron's descendants into groups for 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 The divisions of Aaron's descendants were as follows: Aaron's sons were Nadab and Abihu, Eleazar and Ithamar.

2 Nadab and Abihu died before their father died, and neither had any children. So Eleazar and Ithamar served as priests.

3 David, Eleazar's descendant Zadok, and Ithamar's descendant Ahimelech divided Aaron's descendants into groups for service.

4 Since Eleazar's descendants had more men who were family heads than Ithamar's descendants, they were divided so that Eleazar's descendants had 16 family leaders and Ithamar's descendants had 8 family leaders.

5 Both groups were divided impartially by drawing lots so that there were officers for the holy place and officers for God among both Eleazar's and Ithamar's descendants.