1 Chronicles 21:19 Meaning

17And David said unto God, Is it not I that commanded the people to be numbered? even I it is that have sinned and done evil indeed; but as for these sheep, what have they done? let thine hand, I pray thee, O LORD my God, be on me, and on my father's house; but not on thy people, that they should be plagued.

18Then the angel of the LORD commanded Gad to say to David, that David should go up, and set up an altar unto the LORD in the threshingfloor of Ornan the Jebusite.

19And David went up at the saying of Gad, which he spake in the name of the LORD.

20And Ornan turned back, and saw the angel; and his four sons with him hid themselves. Now Ornan was threshing wheat.

21And as David came to Ornan, Ornan looked and saw David, and went out of the threshingfloor, and bowed himself to David with his face to the ground.