Ezr 6:19-20
The feast of the passover, on the fourteenth day of the first month, took place only a few weeks after the dedication of the temple. The reason given in Ezr 6:20 - for the priests and Levites had purified themselves without exception (כּאחד, like Ezr 3:9); they were all clean, and they killed the passover for all the sons of the captivity (i.e., the laity who had returned from exile), and for their brethren the priests, and for themselves - has in this connection the meaning: Then the congregation celebrated the passover, and they were able to keep and to eat the passover, because the priests had purified themselves that they might be qualified for performing the office incumbent upon them of sprinkling the blood; and the Levites were also clean, that they might be able to kill the lambs for the whole congregation (comp. the remarks on 2Ch 30:17, etc., and 2Ch 35:11, 2Ch 35:14). From the days of Josiah, it seems to have been customary for the Levites to take the place of the heads of families (Exo 12:6, etc.) in slaughtering the passover lambs for the whole community, both priesthood and laity: for the laity, that no person who was unclean might kill the paschal lamb; for the priests, that their labours might be lightened, the sprinkling of blood and the offering of sacrifices occupying them far into the night (2Ch 35:11, 2Ch 35:14-15). And this custom was followed at this time also. The priests are called אחיהם, brethren of the Levites, as in 2Ch 29:34; 2Ch 35:15.