Adam Clarke on Isaiah 18:3

When he lifteth up an ensign "When the standard is lifted up" - I take God to be the Agent in this verse; and that by the standard and the trumpet are meant the meteors, the thunder, the lightning, the storm, earthquake, and tempest, by which Sennacherib's army shall be destroyed, or by which at least the destruction of it shall be accompanied; as it is described in Isa 10:16, Isa 10:17; Isa 29:6, and Isa 30:30, Isa 30:31. See also Psa 76:1-12 (note), and the title of it, according to the Septuagint, Vulgate and Aethiopic. They are called, by a bold metaphor, the standard lifted up, and the trumpet sounded. The latter is used by Homer, I think with great force, in his introduction to the battle of the gods; though I find it has disgusted some of the minor critics: - Βραχε δ' ευρεια χθων, Αμφι δε σαλπιγζεν μεγας ουρανος.

Il. 21:388. "Heaven in loud thunders bids the trumpet sound,

And wide beneath them groans the rending ground."

Pope