Albert Barnes Commentary 1 Chronicles 15:5

"of the sons of Kohath, Uriel the chief, and his brethren a hundred and twenty;" — 1 Chronicles 15:5 (ASV)

The sons of Kohath - The order of Levi’s sons according to birthright is Gershom, Kohath, and Merari (Genesis 46:11; Exodus 6:16). However, the Kohathites, from whom the priestly family of Aaron descended, had precedence in all respects.

They were especially entrusted with attending to and carrying the ark. Of the six Levitical families mentioned in 1 Chronicles 15:5–10, only one was descended from Gershom and one from Merari, while four (Uriel, Elizaphan, Hebron, and Uzziel) were from Kohath.