What does 1 Chronicles 21:15 mean?

God sent an angel to destroy Jerusalem, but as the angel was about to do it, the Lord saw and changed his mind about the disaster. He told the angel, 'Enough—stop now!' The angel was standing by the threshing floor of Ornan the Jebusite. 1 Chronicles 21:15 - Modern Text Bible

(God’s mercy interrupts the destruction, and the location becomes significant for what follows.)