1 Chronicles 24:3

3 King David organized the descendants of Aaron into groups according to their duties. He was assisted in this by Zadok, a descendant of Eleazar, and by Ahimelech, a descendant of Ithamar.

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 are the groups to which the descendants of Aaron belong. Aaron had four sons: Nadab, Abihu, Eleazar, and Ithamar.

2 Nadab and Abihu died before their father did, and left no descendants, so their brothers Eleazar and Ithamar became priests.

3 King David organized the descendants of Aaron into groups according to their duties. He was assisted in this by Zadok, a descendant of Eleazar, and by Ahimelech, a descendant of Ithamar.

4 The descendants of Eleazar were organized into sixteen groups, while the descendants of Ithamar were organized into eight; this was done because there were more male heads of families among the descendants of Eleazar.

5 Since there were Temple officials and spiritual leaders among the descendants of both Eleazar and Ithamar, assignments were made by drawing lots.