1 Chronicles 24:3

3 David, with the help of Zadok, a descendant of Eleazar, and Ahimelech, a descendant of Ithamar, separated their family groups into two different groups. Each group had certain duties.

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 groups of Aaron's sons: Aaron's sons 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 the priests.

3 David, with the help of Zadok, a descendant of Eleazar, and Ahimelech, a descendant of Ithamar, separated their family groups into two different groups. Each group had certain duties.

4 There were more leaders from Eleazar's family than from Ithamar's -- sixteen leaders from Eleazar's family and eight leaders from Ithamar's family.

5 Men were chosen from Eleazar's and Ithamar's families by throwing lots. Some men from each family were chosen to be in charge of the Holy Place, and some were chosen to serve as priests.