II Samuel 13:13

Amnon's Incest, and Absalom's Fratricide - 2 Samuel 13 The judgments threatened to king David in consequence of his sin with Bathsheba soon began to fall upon him and upon his house, and were brought about by sins and crimes on the part of his own sons, for which David was himself to blame, partly because of his own indulgence and want of discipline, and partly because of the bad example that he had set them. Having grown up without strict paternal discipline, simply under the care of their different mothers, who were jealous of one another, his sons fancied that they might gratify their own fleshly lusts, and carry out their own ambitious plans; and from this there arose a series of crimes, which nearly cost the king his life and throne. Amnon, David's eldest son, led the way with his forcible violation of his step-sister Tamar (vv. 1-22). The crime was avenged by her own brother Absalom, who treacherously assassinated Amnon, in consequence of which he was obliged to flee to Geshur and take refuge with his father-in-law (vv. 23-39).

The righteous God had lately told David, by Nathan the prophet, that, to chastise him for his son in the matter of Uriah, he would "raise up evil against him out of his own house," (Sa2 12:11). And here, in the very next chapter, we find the evil beginning to rise; henceforward he was followed with one trouble after another, which made the latter part of his reign less glorious and pleasant than the former part. Thus God chastened him with the rod of men, yet assured him that his "loving-kindness he would not utterly take away." Adultery and murder were David's sins, and those sins among his children (Amnon defiling his sister Tamar, and Absalom murdering his brother Amnon) were the beginnings of his punishment, and the more grievous because he had reason to fear that his bad example might help to bring them to these wickednesses. In this chapter we have, I. Amnon ravishing Tamar, assisted in his plot to do it by Jonadab his kinsman, and villainously executing it (v. 1-20). II. Absalom murdering Amnon for it (v. 21-39). Both were great griefs to David, and the more because he was unwittingly made accessory to both, by sending Tamar to Amnon and Amnon to Absalom.

13:13 he will let you marry me: Tamar said this to gain time; Amnon knew that the law prohibited marriage between half siblings (see study note on 13:2), and he refused to back off.