1 Chronicles 24:3

3 David assigned Zadok from the family of Eleazar and Ahimelech from the family of Ithamar and assigned them to separate divisions for carrying out their appointed ministries.

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 family of Aaron was grouped as follows: Aaron's sons were Nadab, Abihu, Eleazar, and Ithamar.

2 Nadab and Abihu died before their father and left no sons. So Eleazar and Ithamar filled the office of priest.

3 David assigned Zadok from the family of Eleazar and Ahimelech from the family of Ithamar and assigned them to separate divisions for carrying out their appointed ministries.

4 It turned out that there were more leaders in Eleazar's family than in Ithamar's and so they divided them proportionately: sixteen clan leaders from Eleazar's family and eight clan leaders from Ithamar's family.

5 They assigned the leaders by lot, treating both families alike, for there were officials of the sanctuary and officials of God among both the Eleazar and Ithamar families.