The military victory over Moab culminates in a severe and unusual punishment, blending a deep personal reckoning with calculated political strategy. Following the battle, David orders the captive Moabites, specifically the enemy soldiers [ביאור שטיינזלץ], to lie down on the ground side by side. He then measures the men using a physical measuring line [מצודת דוד, ביאור שטיינזלץ]. This process is deliberately designed to shame and humiliate the defeated army [רד״ק, מלבי״ם, אברבנאל], while the measuring itself functions as a method of casting lots to determine their exact fate [רד״ק]. Through this method, David decrees that two-thirds of the captives be put to death, leaving only one-third alive [מצודת ציון, אברבנאל].
The motivation behind this massive execution operates on two distinct levels. The primary approach among commentators points to a matter of historical and personal revenge. Years earlier, while fleeing from King Saul, David sought refuge for his parents and brothers, entrusting them to the care of the King of Moab. The Moabites betrayed this trust and murdered his family, leaving only one brother who managed to escape and find safety with Nahash the Ammonite. The execution of the soldiers serves as David's direct retaliation for that tragic betrayal.
Beyond personal revenge, the decision acts as a practical military strategy meant to permanently break Moab's power and deter other neighboring nations from waging war against Israel [ביאור שטיינזלץ, אברבנאל]. The specific choice to eliminate two-thirds of the men is driven by the sheer size of the captive army. Sparing everyone would create a significant security risk, as the soldiers could easily unite and rebel. At the same time, David avoids total annihilation because he intends to use the survivors as a labor force [אברבנאל]. For this reason, he does not specifically single out the strongest warriors to be spared, since their future role requires no military skill, only servitude and the generation of revenue [מלבי״ם].
Ultimately, the Moabite nation [רד״ק] is entirely subdued and submits to David's authority [ביאור שטיינזלץ]. The survivors are reduced to subjects, bound to pay a regular annual tax to Israel [מצודת דוד, רד״ק, אברבנאל, מלבי״ם].