Albert Barnes Commentary Nahum 1:5

"The mountains quake at him, and the hills melt; and the earth is upheaved at his presence, yea, the world, and all that dwell therein." — Nahum 1:5 (ASV)

The mountains quaked at Him, and the hills melted - As of their own accord. The words are a renewal of those of Amos (Amos 9:13). Inanimate nature is pictured as endowed with the terror, which guilt feels at the presence of God.

All power, whether greater or less, whatever lifts itself up, will give way in that Day, which will be upon all the cedars of Lebanon that are high and lifted up, and upon all the oaks of Bashan, and upon all the high mountains, and upon all the hills that are lifted up (Isaiah 2:13–14).

And the earth is burned (rather lifts itself up; as in an earthquake it seems, as it were, to rise and sink down, lifting itself as if to meet its God or to flee). What is strongest, shakes; what is hardest, melts; indeed, the whole world trembles and is removed:

“If,” said even Jews of old, “when God made Himself known in mercy, to give the law to His people, the world was so moved at His presence, how much more, when He will reveal Himself in wrath!”

The words are so great that they bear the soul on to the time when heaven and earth will flee away from the Face of Him Who sitteth on the throne, and the elements shall melt with fervent heat (Revelation 20:11; 2 Peter 3:10).

And since all judgments are images of the Last, and the awe at tokens of God’s presence is a shadow of the terror of that coming, he adds,