John Gill 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)

These are the divisions of the porters among the sons of Kore,

and among the sons of Merari .

] For among those Levites which descended from Kore, a grandson of Kohath, and which sprung from Merar, a brother of Kohath, the porters only wore; see (1 Chronicles 26:1 1 Chronicles 26:10) .