Albert Barnes Commentary 1 Chronicles 26:19

"These were the courses of the doorkeepers; of the sons of the Korahites, and of the sons of Merari." — 1 Chronicles 26:19 (ASV)

The divisions of the porters—The account of the porters given here states there were only twenty-four on duty at any one time. However, 1 Chronicles 23:5 indicates that this duty was carried out by 4,000 people.

A possible explanation is that the 93 chief porters mentioned in 1 Chronicles 26:8–9, 11, and 24 were always on guard as officers. The remaining 3,907 would then serve in rotation each day as their subordinates.