At the voice of the tumult the peoples fled. He now returns to the former doctrine, or rather he continues it, after having inserted a short exclamation. He had already shewn that the Assyrians would be defeated, though they appeared to be out of the reach of all danger; and now he bids the Jews look upon it as having actually taken place; for their power was vast, and all men dreaded them and reckoned them invincible. Isaiah therefore places before the eyes of the Jews the dreadful ruin of the Assyrians, as if it had been already accomplished. He makes use of the plural number, saying that they were peoples; for the kingdom of the Assyrians consisted of various "peoples," and their army had been collected out of various nations; and therefore he affirms that, although their number was prodigious and boundless, yet they would miserably perish. At thy exaltation. The word "exaltation" is explained by some to mean the "manifestation" by which the Lord illustriously displayed what he was able to do. But I explain it in a more simple manner, that the Lord, who formerly seemed as it were to remain at rest, when he permitted the Babylonians to ravage with impunity, now suddenly came forth to public view; for his delay was undoubtedly treated with proud scorn by the enemies, as if the God of Israel had been humbled and vanquished; but at length he arose and sat down on his judgmentseat, and took vengeance on the crimes of the ungodly. There is therefore an implied contrast between the "exaltation" and that kind of weakness which the Lord appeared to exhibit, when he permitted his people to be afflicted and scattered. [1] By "the voice of the tumult" some suppose to be meant that the Lord will put the enemies to flight by merely making a noise; but that interpretation, I fear, is more ingenious than solid. I therefore willingly interpret the word "voice" to mean the loud noise which would be raised by the Medes and Persians.

Footnotes

1 - The rising meant is not the ascent of the Judge to the judgmentseat, (Piscator,) nor the exaltation of the Assyrian power, (AbenEzra.) but the act of rising from a state of seeming inaction, as when one rouses himself to strike, (Barnes.)" -- Alexander.

At the noise of the tumult - Lowth supposes that this is addressed by the prophet in the name of God, or rather by God himself to the Assyrian, and that it means that notwithstanding the terror which he had caused the invaded countries, he would himself fall and become an easy prey to those whom he intended to subdue. But probably it should be regarded as a part of the address which the Jews made to Yahweh Isaiah 33:2, and the word 'tumult' - המון hâmôn, sound, noise, as of rain 1-Kings 18:41, or of music Ezekiel 26:13; Amos 5:23, or the bustle or tumult of a people 1-Samuel 4:11; 1-Samuel 14:19; Job 39:7 - refers here to the voice of God by which the army was overthrown. Yahweh is often represented as speaking to people in a voice suited to produce consternation and alarm. Thus it is said of the vision which Daniel saw of a man by the side of the river Hiddekel, 'his words' were 'like the voice of a multitude' (המון hâmôn), Daniel 10:6. And thus, in Revelation 1:10, the voice of Christ is said to have been 'like the voice of a trulupet;' and in Isaiah 33:15, 'like the sound of many waters.' It wilt be recollected also that it was said that God would send upon the Assyrian army 'thunder, and an earthquake, and a great noise, with storm and tempest, and a flame of devouring fire' (Isaiah 29:6; compare Isaiah 30:30); and it is doubtless to this prediction that the prophet refers here. God would come forth with the voice of indignation, and would scatter the combined armies of the Assyrian.
The people fled - The people in the army of the Assyrian. A large part of them Were slain by the angel of the Lord in a single night, but a portion of them with Sennacherib escaped and fled to their own land (Isaiah 37:36-37.
At the lifting up of thyself - Of Yahweh; as when one rouses himself to strike.
The nations - The army of Sennacherib was doubtless made up of levies from the nations that had been subdued, and that composed the Assyrian empire.

At the noise of the tumult "From thy terrible voice" - For המון hamon, "multitude," the Septuagint and Syriac read אמיך amica, "terrible," whom I follow.

At the noise of the tumult the (f) people fled; at the (g) lifting up of thyself the nations were scattered.
(f) That is, the Assyrians fled before the army of the Chaldeans, or the Chaldeans for fear of the Medes and Persians.
(g) When you, O Lord, lifted up your arm to punish your enemies.

At the noise of the tumult the people fled,.... The Vulgate Latin Version renders it, "at the voice of the angel"; and Jerom reports it as the opinion of the Jews, that it was Gabriel; and many interpret the words either of the noise the angel made in the air, or was made in the Assyrian camp, when the angel descended, and smote such a vast number of them, at which the remnant, being frightened, fled, 2-Kings 19:35 but either this is to be understood as expressing what had been done in time past, and therefore the church took encouragement that it might and would be so again; or as a continuance of her prayer, thus, "at the noise of the tumult", or multitude (t), "let the people flee" (u); or as a prediction, "they shall flee" (w); that is, at the noise of the multitude of saints, the faithful, called, and chosen armies of heaven, that follow Christ on white horses, and clothed in white; when he shall go forth to battle with the kings of the earth, beast, and false prophet, let the people under them flee, or they shall flee, and not be able to stand before so puissant a General, and so powerful an army; see Revelation 17:14,
at the lifting up of thyself, the nations were scattered; so it has been in times past, when the Lord has lifted up himself, and appeared on behalf of his people, and has exerted himself, and displayed his power; and so it will be again; or so let it be: "let the nations be scattered"; the antichristian nations, as they will be, when the Lord shall lift up his hand, and pour out the vials of his wrath upon them.
(t) "a voce multitudinis", Pagninus; "a voce turbae", Montanus, Cocceius. (u) Fugiant, so some in Gataker. (w) Profugient, Piscator.

the tumult--the approach of Jehovah is likened to an advancing thunderstorm (Isaiah 29:6; Isaiah 30:27), which is His voice (Revelation 1:15), causing the people to "flee."
nation--the Assyrian levies.

While the prophet is praying thus, he already sees the answer. "At the sound of a noise peoples pass away; at Thy rising nations are scattered. And your booty is swept away as a swarm of locusts sweeps away; as beetles run, they run upon it." The indeterminate hâmōn, which produces for that very reason the impression of something mysterious and terrible, is at once explained. The noise comes from Jehovah, who is raising Himself judicially above Assyria, and thunders as a judge. Then the hostile army runs away (נפצוּ = נפצּוּ, from the niphal נפץ, 1-Samuel 13:11, from פּץ = נפוץ, from פּוּץ); and your booty (the address returns to Assyria) is swept away, just as when a swarm of locusts settles on a field, it soon eats it utterly away. Jerome, Cappellus, and others follow the Septuagint rendering, ὃν τρόπον ἐάν τις συναγάγη ἀκρίδας. The figure is quite as appropriate, but the article in hechâsı̄l makes the other view the more natural one; and Isaiah 33:4 places this beyond all doubt. Shâqaq, from which the participle shōqēq and the substantive masshâq are derived, is sued here, as in Joel 2:9, to signify a busy running hither and thither (discursitare). The syntactic use of shōqēq is the same as that of קרא (they call) in Isaiah 21:11, and sōphedı̄m (they smite) in Isaiah 32:12. The inhabitants of Jerusalem swarm in the enemy's camp like beetles; they are all in motion, and carry off what they can.

The noise - Which the angel shall make in destroying the army. The people - Those of the army, who escaped that stroke. The nations - The people of divers nations, which made up this army.