For there were many in the assembly who had not consecrated themselves. Therefore the Levites had to slaughter the Passover lamb for everyone who was not clean, to consecrate it to the Lord. For a majority of the people, many of them from Ephraim, Manasseh, Issachar, and Zebulun, had not cleansed themselves, yet they ate the Passover otherwise than as prescribed. For Hezekiah had prayed for them, saying, “May the good Lord pardon everyone who sets his heart to seek God, the Lord, the God of his fathers, even though not according to the sanctuary's rules of cleanness.” And the Lord heard Hezekiah and healed the people. (2Ch 30:17-20)
Picture the scene. A nation has forsaken God; a people have abandoned his law. But an invitation goes out... an offer from the king to come to the table of the Lord and enjoy his favour.
But there's a problem. The people are not in any state to return to God. They have not kept themselves pure or lived up to the righteous standard required to approach his table. They want to return but know that their own actions now separate them from God.
So the king himself rouses himself on their behalf and makes intercession for them. Although the people are unworthy to return, God hears the priestly prayer of his appointed king and opens up the way so that all who have a heart after God may return. They can come and sit down at the Lord's table without fear and without condemnation.
What Hezekiah did for the people of Israel is a shadow of what Jesus now does for all people.
We were separated from a holy God by our own actions with no way back. But Jesus himself makes intercession for us, and presented himself as the spotless passover lamb to be slain on our behalf. This intercession and sacrifice now holds the door to heaven open so that whoever has a heart towards God may come without guilt or condemnation.
The king's priestly prayer was heard. The way back to God is open.