Albert Barnes Commentary Ezra 6:20

"For the priests and the Levites had purified themselves together; all of them were pure: and they killed the passover for all the children of the captivity, and for their brethren the priests, and for themselves." — Ezra 6:20 (ASV)

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.