1 Chronicles 24:3

3 With the help of Eleazar’s descendant Zadok and Ithamar’s descendant Ahimelech, David divided them according to the offices of 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 These were the divisions of the descendants of Aaron. The sons of Aaron were Nadab, Abihu, Eleazar, and Ithamar.

2 But Nadab and Abihu died before their father did, and they had no sons; so Eleazar and Ithamar served as priests.

3 With the help of Eleazar’s descendant Zadok and Ithamar’s descendant Ahimelech, David divided them according to the offices of their service.

4 Since more leaders were found among Eleazar’s descendants than those of Ithamar, they were divided accordingly. There were sixteen heads of families from the descendants of Eleazar and eight from the descendants of Ithamar.

5 Thus they were divided by lot, for there were officers of the sanctuary and officers of God among both Eleazar’s and Ithamar’s descendants.