In sackcloth, i.e. in mourning garments, humbling themselves before God for their sins, and deprecating his wrath against the people.
Related Commentaries of 1 Chronicles 21:16
1 Chronicles 21:16
16 And David lifted up his eyes, and saw the angel of the LORD stand between the earth and the heaven, having a drawn sword in his hand stretched out over Jerusalem. Then David and the elders of Israel, who were clothed in sackcloth, fell upon their faces.