1 Chronicles 24:1

“Now these are the divisions of the sons of Aaron, etc.] Into the classes or courses following: the sons of Aaron; Nadab and Abihu, Eleazar and Ithamar; (<130603>1 Chronicles 6:3), these were the immediate sons of Aaron; but the division or distribution of them into classes are of their posterity in the times of David, who descended from the two latter.”

“DIVISION OF THE SONS OF AARON INTO FOUR AND TWENTY ORDERS. (1Ch. 24:1-19) Now these are the divisions of the sons of Aaron--(See on Ch1 23:6).”

“Divisions - The several branches into which that family was divided. 1 Chronicles 24:2”

“24:1-19 The information about the priests’ duties includes only their organization into orders and the assignment of their responsibilities by casting lots. The Chronicler does not explain their duties because they had long been solidly established (see Exod 28:1-5; Lev 1–7; Num 6:22-27). 24:1-2 The organization of the priests into their divisions for service began with Aaron’s sons Eleazar and Ithamar; all of Israel’s priests were descended from these two men.”

“the divisions: Ch1 23:6 \*marg. The sons: Ch1 6:3; Exo 6:23, Exo 28:1; Lev 10:1-6; Num 3:2, Num 26:60 1 Chronicles 24:2”

“The division of the priests and Levites into classes. - Vv. 1-19. The twenty-four classes of priests. After the statement as to the fathers'-houses of the Levites (1 Chron 23), we have next the arrangements of the priests for the performance of the service in the sanctuary; the priestly families descended from Aaron's sons Eleazar and Ithamar being divided into twenty-four classes, the order of whose service was settled by lot. Ch1 24:1 contains the superscription, "As for the sons of Aaron, their divisions (were these)." To make the division clear, we have an introductory notice of Aaron's descendants, to the effect that of his four sons, the two elder, Nadab and Abihu, died before their…”