Chronicles records a crisis during Hezekiah's Passover: many worshipers were ceremonially unclean, so the Levites took responsibility for 'the slaughtering of the Passover lambs' on their behalf. This construct phrase turns the verbal action (slaughtering) into a nominal concept (the act of slaughtering). The Passover ritual required specific procedures for killing and preparing the lamb, and this noun captures that technical sacrificial action. Who performed the slaughter mattered—hence the Levites' intervention.