The sudden collapse of a mighty empire sends shockwaves in every direction, leaving its allies and dependents completely helpless. Through the vivid metaphor of a massive cedar of Lebanon violently cut down and plunging into the abyss, the absolute downfall of the King of Assyria is depicted. This descent into the grave marks the exact moment God humbles the mighty ruler, signaling the total destruction of his empire [רש״י, מצודת דוד, מצודת ציון, ביאור שטיינזלץ].
With the king's fall, the very source of his life and power is reversed. The deep, abundant waters that once symbolized the divine nourishment that elevated Assyria now become associated with ruin and mourning [רד״ק, אברבנאל]. The primary approach among commentators is that the deep itself is personified, mourning the collapse of the great cedar by covering its face in sackcloth and refusing to water the surrounding trees [רד״ק, מצודת דוד, מלבי״ם]. Conversely, others explain that God actively uses the deep to cover and drown the falling cedar, effectively destroying all those who aided the empire [אברבנאל, רש״י]. Consequently, God halts the flow of these rivers, as their nourishment is no longer needed [מצודת דוד, אברבנאל]. The waters are restrained by force, imprisoned within the deep against their natural tendency to flow [מלבי״ם, מצודת ציון, ביאור שטיינזלץ].
The impact of this monumental fall is immediately felt throughout the surrounding environment. Because the King of Assyria is likened to a cedar, his destruction causes the entire forest of Lebanon to turn dark and gloomy [רד״ק, רש״י, מצודת ציון]. This darkness can be understood as the physical blackening and withering of the trees from heat and severe drought in the absence of water [מלבי״ם], or as a profound expression of grief and depression over the cedar's demise [מצודת דוד, ביאור שטיינזלץ].
Furthermore, the lesser trees of the field, representing the ministers, warriors, and subordinate kings who once thrived under Assyria's protection, are left utterly devastated [רש״י, מצודת דוד, מלבי״ם]. Stripped of their life source, these dependent nations collapse into a state of extreme weakness and fainting [מצודת ציון, רד״ק]. Their collapse stems either from literal dehydration after being cut off from their water supply [רש״י, מלבי״ם], or from the sheer terror and panic that grips them upon witnessing the bitter fate of their invincible leader [אברבנאל, מצודת דוד, ביאור שטיינזלץ]. This entire chain of disasters is orchestrated directly by God, demonstrating His absolute control over the fate of all nations [רד״ק].