Matthew Henry on 2 Chronicles 30:13-20

The great thing needful in attendance upon God in solemn ordinances, is, that we make heart-work of it; all is nothing without this. Where this sincerity and fixedness of heart are, there may yet be many things 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 should deal with us in strict justice, even as to the very best of our doings, we should be undone. The way to obtain pardon, is to seek it of God by prayer; it must be gotten by petition through the blood of Christ. Yet every defect is sin, and needs forgiveness; and should be matter to humble, but not to discourage us, though nothing can make up for the want of a heart prepared to seek the Lord.