Chronicles I 24:3

3 And David distributed them, even Sadoc of the sons of Eleazar, and Achimelech of the sons of Ithamar, according to their numbering, according to their service, according to the houses of their fathers.

Chronicles I 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.

Chronicles I 24:3 In-Context

1 And the sons of Aaron in division, Nadab, and Abiud, and Eleazar, and Ithamar.

2 And Nadab and Abiud died before their father, and they had no sons: so Eleazar and Ithamar the sons of Aaron ministered as priests.

3 And David distributed them, even Sadoc of the sons of Eleazar, and Achimelech of the sons of Ithamar, according to their numbering, according to their service, according to the houses of their fathers.

4 And there were found the sons of Eleazar more chiefs of the mighty ones, than of the sons of Ithamar: and he divided them, sixteen heads of families to the sons of Eleazar, eight according to families to the sons of Ithamar.

5 And he divided them according to their lots, one with the other; for there were those who had charge of the holy things, and those who had charge of the of the Lord among the sons of Eleazar, and among the sons of Ithamar.