i.e. With that ceremonial purification which was required of them that came into God's sanctuary. So he calls it, to distinguish from that moral and internal purity which they are here acknowledged to have.
Related Commentaries of 2 Chronicles 30:19
2 Chronicles 30:19
19 That prepareth his heart to seek God, the LORD God of his fathers, though he be not cleansed according to the purification of the sanctuary.