God sent an angel to Jerusalem to destroy it: and as he was about to destroy, Yahweh saw, and he repented him of the evil, and said to the destroying angel, It is enough; now stay your hand. The angel of Yahweh was standing by the threshing floor of Ornan the Jebusite.
Now this must have been really something for David. He saw up there in the sky the angel of the Lord with a drawn sword. It must have been a very frightening experience, to say the least. 