When God Speaks in Judgement
Nahum 1:5 (ESV) … “The mountains quake before him; the hills melt; the earth heaves before him, the world and all who dwell in it.”
All the ‘mountains’, both great and small, tremble before his presence and power. At his rebuke they rock to and fro and sway like a reed in the wind (cf. Judges 5:4; Job 9:5–6; Jeremiah 4:24; Isaiah 24:18–20). These quaking mountains are descriptive either of the vibrating effect of thunder or perhaps of an earthquake or volcanic disturbance.
The very foundations of the earth shake when God speaks, ‘… and the hills melt away’; that is, as wax before a flame or snow in the midday sun, so the hills shrink before the scorching heat of his word (cf. Micah 1:4; Psalm 97:3–5). Through vivid imagery inanimate nature is pictured as endowed with the terror which guilt feels at the presence of God. Assyria’s doom is sealed; for if the strongest mountains ‘quake’ and lifeless hills ‘melt away’ before the Lord, what hope have the Assyrians, and sinners in general, of standing unmoved before his wrath? (cf. Revelation 6:16–17).
At the manifestation of his ‘presence’ and glory, the whole ‘earth trembles’. The verb ‘to tremble’ means either ‘to lay waste’, ‘to give way’ or more probably ‘to lift up’. The prophet, alluding to both an earthquake and the final judgement, pictures the earth ‘and all who live in it’, man and beast, as heaving violently and in terror before the Lord. As a ship is thrown up and down by the raging sea, so the earth and its inhabitants tremble (cf. Exodus 19:16; 20:18; Hebrews 12:21) as they rise and fall under the judgements of God.
 Shenton, T. (2007). Nahum and Obadiah: an expositional commentary (pp. 26–27). Day One Publications.