The revelation of God in the world is an event of such overwhelming power and terror that even the most massive, solid elements of nature lose their form. The towering mountains melt away like wax [רש״י, רד״ק, מצודת ציון, שטיינזלץ]. Although mountains are naturally dry and rigid, they dissolve completely contrary to their physical nature. This dramatic breakdown is driven by the sheer terror brought on by the presence of God [אבן עזרא, שטיינזלץ] and the fiery lightning of His providence [מלבי״ם]. This awe-inspiring scene is understood to be a future event destined to unfold [מאירי].
While some view this destruction literally, as physical mountains collapsing and falling [רש״י, מלבי״ם], the primary approach among commentators is to read this as a powerful metaphor. In this view, the towering mountains represent proud, arrogant individuals, as well as the wicked kings and leaders of the nations. Faced with God, their power and pride simply melt away from fear [רד״ק, אבן עזרא, מצודת דוד, מאירי]. This collapse does not require a direct physical strike, as the melting happens simply from the natural spread of the radiance of His presence [אלשיך].
Ultimately, this display of power serves to establish God as the absolute Master of the entire world. This reality directly confronts the arrogant leaders, proving that despite their grand thoughts, they do not truly rule the earth [אבן עזרא]. Furthermore, the dramatic breakdown of nature serves to completely disprove the beliefs of idolaters, who imagine that different stars or local idols control specific regions. The melting of the world's most permanent fixtures proves to everyone that the forces of nature do not operate independently. God alone is the single, absolute Lord of the entire earth [מלבי״ם].