3,915. The Duty Watches of Kohanim

Hilchos Klei HaMikdash 4:3

Moshe divided the kohanim into eight duty watches – four from Aaron’s son Elazar and four from Aaron’s son Itamar. These watches continued into the time of Samuel, who, with King David, divided them into 24 watches. Each watch had one member who served as leader. A watch would go to Jerusalem to serve for the whole week, changing rosters on Shabbos. At that time, the old watch would exit and the new watch would enter. They went on in this way until all the watches had served, at which point they would begin again.

Hilchos Klei HaMikdash 4:4

There is a Torah obligation that all the watches are equal during the three Festivals. Any kohein who comes during a Festival and wants to serve may do so and receive a share of the offerings; he is not told to wait until his watch’s turn arrives. Regarding this, Deuteronomy 18:6 says, “When the Levi (referring to a kohein) comes from one of your cities....”