What is "Arbatayim"?
Targum Yonasan: It is four-fold. Rashi, from Yuma 22b - and so David was punished, [with afflictions via] four children - the child [with whom Bas Sheva was pregnant], Amnon, Tamar 1 and Avshalom.
Radak (1): It is eight, twice the four that a thief [who slaughtered the lamb that he stole] pays. An Ashir who stole from an Oni should be fined to pay extra!
Malbim (Divrei ha'Yamim I, 3:6): Tamar is not counted, for she did not die! Also the baby is not among the four, for it says explicitly "the son born to you will die" (verse 14). Rather, Divrei ha'Yamim I, 3:5-8 counts nine sons born to David in Yerushalayim. Above (5:15-16) Nogah and [one of the sons named] Elifelet are omitted, for they died.
Why did he say "Asher Asah
Malbim: He will pay four lambs, like Torah law, for his action, and he will die [according to the king's law] for not having mercy.
