Charles Ellicott 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. — These are the courses of the porters, belonging to the sons of the Korhite, and to the sons of Merari. This concluding remark proves that only the Kohathite and Merarite divisions of Levi had part in the duty of Temple-warders. The Gershonites were not represented among the porters (see 1 Chronicles 26:1; 1 Chronicles 26:10).