The angel commanded that David should go and set up an altar This command was a blessed token of reconciliation. For if God had been pleased to kill him, he would not have commanded, because he would not have accepted, a sacrifice at his hands.
Related Commentaries of 1 Chronicles 21:18
1 Chronicles 21:18
18 Then 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.