Jamieson, Fausset and Brown on 2 Chronicles 35:10-11

10-11. So the service was prepared, &c.--All the necessary preparations having been completed, and the appointed time having arrived for the passover, the solemnity was celebrated. One remarkable feature in the account is the prominent part that was taken by the Levites in the preparation of the sacrifices; namely, the killing and stripping of the skins, which were properly the peculiar duties of the priests; but as those functionaries were not able to overtake the extraordinary amount of work and the Levites had been duly sanctified for the service, they were enlisted for the time in this priestly employment. At the passover in Hezekiah's time, the Levites officiated in the same departments of duty, the reason assigned for that deviation from the established rule being the unprepared state of many of the people (2Ch 30:17). But on this occasion the whole people had been duly sanctified, and therefore the exceptional enlistment of the Levites' services must have been rendered unavoidably necessary from the multitudes engaged in celebrating the passover.