Thes were the divisions of the sons of Aaron. The sons of Aaron: Nadab and Abihu, Eleazar and Ithamar.
Due to the fact that many thousands of the Levites were eligible to participate in the temple services, it was necessary that some systematic manner of determining the order in which they would serve was required. One must be impressed with the manner of David's making such a determination by lot, duly witnessed by all parties concerned.