דברי הימים ב, פרק כ׳, פסוק כ״ב

The battle takes a sudden and miraculous turn the exact moment the people of Judah raise their voices in song and praise to God [מלבי״ם, ביאור שטיינזלץ]. Instead of a conventional clash of armies, a stunning reversal unfolds within the opposing coalition of Ammon, Moab, and Mount Seir, leaving the enemy forces struck and severely weakened by a devastating ambush [מצודת דוד, ביאור שטיינזלץ].

The nature of this ambush reveals the fragile reality of the enemy forces. One approach suggests that God places the inspiration within the hearts of an unidentified group of attackers to lie in wait and strike the camp [מצודת דוד]. Because the invading army is a patchwork coalition of three distinct nations, it lacks the organization and unity required to defend against sudden surprise attacks coming from multiple directions [ביאור שטיינזלץ].

Alternatively, the ambush is understood to have taken place entirely within the enemy camp itself, with God causing the coalition members to turn on one another [רש״י, מלבי״ם]. Beneath the surface, these three nations harbor a deep-seated mutual hatred, having only temporarily set aside their hostility to fight the Israelites. Capitalizing on this bitter rivalry, God orchestrates a deadly internal plot driven by Moab. First, the forces of Moab secretly conspire with the men of Mount Seir to ambush and strike the army of Ammon. Once Ammon is defeated and weakened, Moab abruptly switches allegiances, making peace with the Ammonite survivors. Together, this newly formed alliance of Moab and Ammon rises up to completely destroy the forces of Mount Seir [מלבי״ם, רש״י].