The Levites were purified together - They were all ready at one time to observe the proper rites and ceremonies, and had no need of having a second passover, which was appointed by the law for those who had been accidentally defiled, or were at a distance from the tabernacle. See 2 Chronicles 30:3.
Some render, “And the priests were purified; and the Levites, as one man, were all of them pure.” A contrast is drawn between the universal purity of the Levites and the merely general purity of the priests 2 Chronicles 29:34; 2 Chronicles 30:3, which made it fitting that the former should undertake the slaughter of all the Paschal lambs, even of those which the priests were to consume. In later times the ordinary practice was for each head of a family to kill for himself.