Charles Spurgeon Commentary 1 Chronicles 21:15-16

"And God sent an angel unto Jerusalem to destroy it: and as he was about to destroy, Jehovah beheld, and he repented him of the evil, and said to the destroying angel, It is enough; now stay thy hand. And the angel of Jehovah was standing by the threshing-floor of Ornan the Jebusite. And David lifted up his eyes, and saw the angel of Jehovah standing between earth and heaven, having a drawn sword in his hand stretched out over Jerusalem. Then David and the elders, clothed in sackcloth, fell upon their faces." — 1 Chronicles 21:15-16 (ASV)

And the angel of the LORD stood by the threshingfloor of Ornan the Jebusite. 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.

This was the very best clothing and the very best posture for men who were under the chastising hand of God; they had put on sackcloth, and they had fallen upon their faces. O guilty sinner, if God's sword of vengeance is drawn against you, you cannot do better than put sackcloth upon your soul, if not upon your body, and prostrate yourself before the Most High.