20 Her brother Absalom said to her, "Has your brother Amnon had his way with you? Now, my dear sister, let's keep it quiet - a family matter. He is, after all, your brother. Don't take this so hard." Tamar lived in her brother Absalom's home, bitter and desolate.
21 King David heard the whole story and was enraged, 22 but he didn't discipline Amnon. David doted on him because he was his firstborn. Absalom quit speaking to Amnon - not a word, whether good or bad - because he hated him for violating his sister Tamar.
Matthew Henry's Commentary on 2 Samuel 13:20-22
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.
Commentary on 2 Samuel 13:21-29
(Read 2 Samuel 13:21-29)
Observe the aggravations of Absalom's sin: he would have Ammon slain, when least fit to go out of the world. He engaged his servants in the guilt. Those servants are ill-taught who obey wicked masters, against God's commands. Indulged children always prove crosses to godly parents, whose foolish love leads them to neglect their duty to God.