Matthew Henry Commentary 2 Chronicles 30:13-20

"And there assembled at Jerusalem much people to keep the feast of unleavened bread in the second month, a very great assembly. And they arose and took away the altars that were in Jerusalem, and all the altars for incense took they away, and cast them into the brook Kidron. Then they killed the passover on the fourteenth [day] of the second month: and the priests and the Levites were ashamed, and sanctified themselves, and brought burnt-offerings into the house of Jehovah. And they stood in their place after their order, according to the law of Moses the man of God: the priests sprinkled the blood [which they received] of the hand of the Levites. For there were many in the assembly that had not sanctified themselves: therefore the Levites had the charge of killing the passovers for every one that was not clean, to sanctify them unto Jehovah. For a multitude of the people, even many of Ephraim and Manasseh, Issachar and Zebulun, had not cleansed themselves, yet did they eat the passover otherwise than it is written. For Hezekiah had prayed for them, saying, The good Jehovah pardon every one that setteth his heart to seek God, Jehovah, the God of his fathers, though [he be] not [cleansed] according to the purification of the sanctuary. And Jehovah hearkened to Hezekiah, and healed the people." — 2 Chronicles 30:13-20 (ASV)

The essential thing when attending to God in solemn ordinances is that we make it a work of the heart; all else is nothing without this. Even when this sincerity and steadfastness of heart are present, many things may still fall short of the purification of the sanctuary. These defects need pardoning, healing grace; for omissions in duty are sins, as well as omissions of duty.

If God were to deal with us in strict justice, even concerning the very best of our actions, we would be ruined. The way to obtain pardon is to seek it from God by prayer; it must be obtained by petition through the blood of Christ. Yet every defect is sin and needs forgiveness; and this should be a reason to humble us, but not to discourage us, though nothing can compensate for the lack of a heart prepared to seek the Lord.