I Chronicles 24:31

These likewise cast lots over against their brethren, the sons of Aaron,.... These, being divided into twenty four classes also, cast lots, which class should answer to, attend upon, and serve the first course of the priests, and which the second, and so on. And this they did in the same solemn and public manner as the priests had done: in the presence of David the king, and Zadok, and Ahimelech, and the chief of the fathers of the priests and Levites; as in Ch1 24:6. even the principal fathers over against their younger brethren; the sense is, either that the one stood over against the other, to be distributed by lot, the one as well as the other; or they were chosen by lot, let it fall as it would, without any regard to age or dignity, to the seniority or largeness of houses and families; but as they were chosen, be they younger or elder, richer or poorer, their families more or less numerous and ancient, so they took their places. Next: 1 Chronicles Chapter 25

This chapter gives us a more particular account of the distribution of the priests and Levites into their respective classes, for the more regular discharge of the duties of their offices, according to their families. I. Of the priests (v. 1-19). II. Of the Levites (Ch1 24:20-31).

24:31 The Levites were organized according to the same principles as the priests (24:5-6).