3 But Amnon had a friend whose name was Jonadab the son of Shimeah, David's brother. Now Jonadab was a very crafty man. 4 And he said to him, "Why are you, the king's son, becoming thinner day after day? Will you not tell me?" Amnon said to him, "I love Tamar, my brother Absalom's sister." 5 So Jonadab said to him, "Lie down on your bed and pretend to be ill. And when your father comes to see you, say to him, 'Please let my sister Tamar come and give me food, and prepare the food in my sight, that I may see it and eat it from her hand.' " 6 Then Amnon lay down and pretended to be ill; and when the king came to see him, Amnon said to the king, "Please let Tamar my sister come and make a couple of cakes for me in my sight, that I may eat from her hand."
Matthew Henry's Commentary on 2 Samuel 13:3-6
Commentary on 2 Samuel 13:1-20
(Read 2 Samuel 13:1-20)
From henceforward David was followed with one trouble after another. Adultery and murder were David's sins, the like sins among his children were the beginnings of his punishment: he was too indulgent to his children. Thus David might trace the sins of his children to his own misconduct, which must have made the anguish of the chastisement worse. Let no one ever expect good treatment from those who are capable of attempting their seduction; but it is better to suffer the greatest wrong than to commit the least sin.