Notes on the Bible, by Albert Barnes, [1834], at sacred-texts.com
Zadok and Ahimelech (rather Abiathar, see Ch1 24:6) assisted David in drawing up the priestly courses, as the "captains of the host" assisted him in making the divisions of the singers Ch1 25:1.
One sort with another - i. e., "the assignment of their order in the courses was made by lot to the families belonging to Eleazar, and to the families belonging to Ithamar, equally." Both houses had furnished functionaries of the highest class, and therefore no preference was now given to either over the other.
Wrote them before the king - i. e., "wrote down their names as the lots were drawn forth."
Ahimelech the son of Abiathar - A wrong reading. It should be "Abiathar, the son of Ahimelech." See the Sa2 8:17 note.
These were the orderings ... - i. e., "this was the numerical order fixed for their ministerial attendance in the house of the Lord - an attendance which was after the manner determined for them by their forefather Aaron, according to instructions which he received from God."
The object of this second enumeration of the Levitical families (compare 1 Chr. 23:7-23) seems to be the designation of the heads of the families in David's time. The omission of the Gershonites is curious, and can only be accounted for by supposing that the author did not find any account of their heads in his authorities. The addition to the Merarites Ch1 24:26-27 is also curious. It brings the number of families up to twenty-five, which is one more than we should have expected.
Neither "Hebron" nor "the first" is found in the present Hebrew text; but they seem to have been rightly supplied by our translators from Ch1 23:19. The four persons named appear to have been contemporaries of David, the heads of the Hebronite houses in his time (compare Ch1 26:31).
The sons of Jaaziah, Beno - Beno is not really a name. It is the Hebrew for "his son," and is to be attached to Jaaziah. Translate Ch1 24:27, "and the sons of Merari by Jaaziah his son (were) Shoham and Zaccur, and Ibri." The meaning of the whole passage Ch1 24:26-30 seems to be that there were three branches of the Merarites the Beni-Mahli, the Beni-Mushi, and the Beni-Jaaziah.
The principal fathers over against their younger brethren - i. e., "all the Levitical houses enumerated drew lots in their courses on equal terms, the older families having no advantage over the younger ones." As there were 24 courses of the priests, so we must suppose that there were 24 of the Levites, though the number of the families as given in the text 1 Chr. 23:7-23; Ch1 24:20-30 is 25.