Matthew Poole and continuators on Isaiah 64:3

3 When thou didst terrible things which we looked not for , thou camest down, the mountains flowed down at thy presence.

This may relate to what he did among the Egyptians, though it be not recorded, and afterward in the Wilderness.

viz. Our Forefathers, of whose Race we are, before we expected them; or, such things as we could never expect.

q. d. Seeing thou hast made the Mountains thus to melt, thou canst do the same again: This may allude either, 1. To those showers of Rain that fell with that terrible Thunder and Lightning, and so ran violently down those Mountains, and the adja[illegible: 1+ letters]nt, as is usual in such Tempests: Or rather, 2. The running along of the fire upon the ground, Exod. 9. 23, 24. It is possible it may allude to those Mountains, that do cast forth sulphoreous matter, running down into the Valleys and Sea, like melted streams of fire. And Kings, Princes, and Potentates, may also metaphorically be understood by these Mountains.

Marginal references: Exo. 34. 10. Judg. 5. 4, 5. Psal. 63. 8. Hab. 3. 3.