KJV:
For there were many in the congregation that were not sanctified: therefore the Levites had the charge of the killing of the passovers for every one that was not clean, to sanctify them unto the LORD.
NASB:
For there were many in the assembly who had not consecrated themselves; therefore, the Levites were over the slaughter of the Passover lambs for everyone who was unclean, in order to consecrate them to the LORD.