26 Now Joab was fighting against Rabbah, in the land of the children of Ammon, and he took the water-town. 27 And Joab sent men to David, saying, I have made war against Rabbah and have taken the water-town. 28 So now, get the rest of the people together, and put them in position against the town and take it, for if I take it, it will be named after my name. 29 Then David got all the people together and went to Rabbah and made war on it and took it. 30 And he took the crown of Milcom from his head; the weight of it was a talent of gold, and in it were stones of great price; and it was put on David's head. And he took a great store of goods from the town.
Matthew Henry's Commentary on 2 Samuel 12:26-30
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.