Since there were many in the assembly who had not consecrated themselves, the Levites were in charge of slaughtering the Passover lambs for every unclean person to consecrate the lambs to the LORD.
The time appointed for the passover having arrived, a very great congregation came together upon the occasion, Ch2 30:13. Now here we have, I. The preparation they made for the passover, and good preparation it was: They took away all the idolatrous altars that were found, not only in the temple, but in Jerusalem, Ch2 30:14. Before they kept the feast, they cast out this old leaven.
Commenting on 2 Chronicles 30:13-20
For a multitude of the people, even many of Ephraim and Manasseh, Issachar and Zebulun,.... All which were of the ten tribes, where idolatry had prevailed for a long time: had not cleansed themselves; from impurity contracted by idolatry and other things: yet did they eat the passover otherwise than it was written; because they ate it in their uncleanness, which was not according to...
2Ch 30:16-17 Standing in their place, according to their right, i.e., according to the prescribed arrangement (see on 1Ch 6:17), the priests sprinkled the blood (of the paschal lambs) from the hand of the Levites, they handing it to them.
Commenting on 2 Chronicles 30:16-17