31 David emptied the city of its people and put them to slave labor using saws, picks, and axes, and making bricks. He did this to all the Ammonite cities. Then David and the whole army returned to Jerusalem.

Matthew Henry's Commentary on 2 Samuel 12:31

Commentary on 2 Samuel 12:26-31

(Read 2 Samuel 12:26-31)

To be thus severe in putting the children of Ammon to slavery was a sign that David's heart was not yet made soft by repentance, at the time when this took place. We shall be most compassionate, kind, and forgiving to others, when we most feel our need of the Lord's forgiving love, and taste the sweetness of it in our own souls.