1 Chronicles 24:3

3 And David assigned them, both Zadok of the sons of Eleazar and Ahimelech of the sons of Ithamar, according to their offices 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 Now these are the divisions of the sons of Aaron. The sons of Aaron: Nadab, and Abihu, Eleazar, and Ithamar.

2 But Nadab and Abihu died before their father and had no children; therefore Eleazar and Ithamar executed the priest's office.

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

4 And there were more chief men found of the sons of Eleazar than of the sons of Ithamar, and thus were they divided. Among the sons of Eleazar there were sixteen chief men of the house of their fathers, and eight among the sons of Ithamar according to the house of their fathers.

5 Thus were they divided by lot, one sort with another, for the governors of the sanctuary and governors of the house of God were of the sons of Eleazar and of the sons of Ithamar.