3 But Amnon had a very crafty friend-his cousin Jonadab. He was the son of David's brother Shimea. 4 One day Jonadab said to Amnon, "What's the trouble? Why should the son of a king look so dejected morning after morning?" So Amnon told him, "I am in love with Tamar, my brother Absalom's sister." 5 "Well," Jonadab said, "I'll tell you what to do. Go back to bed and pretend you are ill. When your father comes to see you, ask him to let Tamar come and prepare some food for you. Tell him you'll feel better if she prepares it as you watch and feeds you with her own hands." 6 So Amnon lay down and pretended to be sick. And when the king came to see him, Amnon asked him, "Please let my sister Tamar come and cook my favorite dish as I watch. Then I can eat it from her own hands."
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.