This verse most clearly proves that Jeremiah was God's herald, and that his language was under the guidance of the celestial Spirit; for he sets forth the manner in which Babylon was taken, as though he had witnessed it with his own eyes. He says that the fords were taken, and that the pools were burnt with fire. We do not read that Cyrus had made use of fire; and some render pools, reeds, but there is no reason to constrain us so to render the word; for the Prophet speaks metaphorically. Their object was to give a literal rendering, by saying that reeds were burnt; but the Prophet shows, speaking hyperbolically, that the fords of the Euphrates were dried up, as though one burned wood by applying fire to it. This, indeed, is not suitable to water; but he, by a hyperbole, expresses more fully the miracle which might have otherwise exceeded human comprehension. He then says, that the fords were dried up, and then adds, that the pools were burnt. The same thing is expressed twice, but in a different way; and as I have already said, he states hyperbolically, that such was the skill of Cyrus and his army, that he made dry the fords and the pools, as though one collected a large heap of wood and consumed it with fire. [1] We now perceive the design of the Prophet. He afterwards adds, that the men of war were broken in pieces For though the fords were made dry, that is, the streams which were drawn from the Euphrates, vet. the guards of the city might have still kept possession of a part of it, and have manfully resisted, so as to prevent the soldiers of Cyrus from advancing farther; but the city was so craftily taken, that the Babylonians were so terrified as not to dare to raise up a finger, when yet they might have defended a part of the city, though one part of it was taken.

Footnotes

1 - The word 'gmym, properly pools, is probably a metonomy for what they grow, even reeds or bulrushes, especially as the same word, in somewhat another form, 'gmn, clearly means a reed. See Isaiah 9:14; Isaiah 19:15. But what these reeds were, authors are at a loss to know. It is said in the thirtieth verse, that they "burnt her habitations;" may it not have been, that they were such as were made of reeds? Then the whole verse appears intelligible; the passages (that is, the entrances from the river, whose streams were diverted) were seized on, and such houses as were in part built of reeds were set on fire; hence the men were frightened. -- Ed

The passages are stopped - The ferries are seized, occupied. The historians state that when Cyrus captured the city his troops moved down the bed of the river and occupied all these ferries, finding at each of them the gates negligently left open. See the Daniel 5:1 note.
The reeds - literally, the marshes or pools, which formed an important part of the defenses of Babylon, were dried up as completely as a piece of wood would be consumed by fire.

That the passages are stopped - Either the bridges or slips for boats, by which the inhabitants passed from one side to the other, and may mean the principal gates or passes in the city, which the victorious army would immediately seize, that they might prevent all communication between the inhabitants.
The reeds they have burned with fire - What this means I cannot tell, unless it refer to something done after the taking of the city. Setting fire to the reeds in the marshy ground, in order the better to clear the places, and give a freer passage to the water, that it may neither stagnate nor turn the solid ground into a marsh. Dr. Blayney thinks it refers to the firing of the houses, in order to throw the inhabitants into the greater confusion; but no historian makes any mention of burning the city, except what is said Jeremiah 51:30, "They have burned her dwelling places;" and this may be a poetical expression. That they burnt nothing before they took the city must be evident from the circumstance of their taking the city by surprise, in the night time, with the greatest secrecy. Still there might have been some gates, barricadoes, or wooden works, serving for barracks or such like, which obstructed some of the great passages, which, when they had entered, they were obliged to burn, in order to get themselves a ready passage through the city. This is the more likely because this burning of reeds is connected with the stopping of the passages, burning the dwelling places, and breaking the bars.

And that the passages are stopped,.... Or "taken", or "seized" (o); where Cyrus placed soldiers to keep them; these were the passages leading from the river Euphrates to the city, the keys of it; the little gates, that Herodotus (p) speaks of, leading to the river, which were left open that night. Kimchi thinks the towers built by the river side, to keep the enemy out, that should attempt to enter, are meant; these were now in his hands;
and the reeds they have burnt with fire; which grew upon the banks of the river, and in the marshes adjoining to it. Some render it, "the marshes" (q); that is, the reeds and bulrushes in them, which usually grow in such places. And Herodotus (r) makes mention of a marsh Cyrus came to; the reeds in it he burnt, having many torches, with which he might set fire to them; as he proposed with them to burn the houses, doors, and porches (s); either to make way for his army, which might hinder the march of it; or to give light, that they might see their way into the city the better: though some think it was to terrify the inhabitants; which seems not so likely, since he marched up to the royal palace with great secrecy. This circumstance is mentioned, to show the certainty of the enemy's entrance, and the taking of part of the city. R. Jonah, from the Arabic language, in which the word (t) here used signifies "fortresses", so renders it here;
and the men of war are affrighted; and so fled, and left the passes, towers, and fortresses, which fell into the hands of Cyrus, as soon as they perceived his army was come up the channel and was landed, and the reeds were burnt.
(o) "praeoccupata", V. L. "comprehensa", Montanus; "occupati", Tigurine version, Schmidt. (p) L. 1. sive Clio, c. 191. (q) "paludes", V. L. Syr. Grotius; "stagna", Junius & Tremellius, Piscator, Schmidt. (r) L. 1. sive Clio, c. 191. (s) Xenophon, Cyropaedia, l. 7. c. 22. (t) "arundinetum feris et hinc munimentum, castellum", Camus apud Golium, col. 33. "castellum, munimentum viarum, arces", Castel. Lex. col. 29.

passages are stopped--The guarded fords of the Euphrates are occupied by the enemy (see on Jeremiah 50:38).
reeds . . . burned--literally, "the marsh." After draining off the river, Cyrus "burned" the stockade of dense tree-like "reeds" on its banks, forming the outworks of the city's fortifications. The burning of these would give the appearance of the marsh or river itself being on "fire."

Permits of being taken as a continuation of the message brought to the king. מעבּרות, "crossing-places," do not here mean "fords" (Judges 3:28); for such shallow places, where one could go through the river, are not to be found in the Euphrates. at Babylon: they mean bridges and ferries, because, in addition to the stone bridge built by Nebuchadnezzar (Herodotus, i. 186; see Duncker's Geschichte, i. S. 859), there must also have been at Babylon, throughout its large extent, other means of crossing, either by bridges of boats or ferries. נתפּשׁוּ, "they have been taken," seized by the enemy; cf. Jeremiah 48:41. אגמּים are ponds and artificial lakes which had been formed for the protection of the city, of the waters of the Euphrates (Herodotus, i. 185; Arrian. Jeremiah 7:17); these "they have burned with fire." Inasmuch as a burning of ponds is an impossibility, many, with Kimchi, would understand אגמים of the reeds of the marshes. But the word has no such meaning; moreover, even if it had, the burning of the reeds would have no significance for the taking of the city. Others think of the sluices and the enclosures of the artificial waters, which enclosures were constructed of wood-work; but apart from the basin of water at Sepharvaim, which could be opened by sluices, the enclosure of the ponds with wood-work is a matter of much doubt, and a burning of the wood-work is not a burning of the ponds. The expression, as Calvin long ago remarked, is hyperbolic, and not to be pressed: Propheta hyperbolice ostendit, siccata fuisse vada Euphratis ac si quis lignum exureret igni supposito; hoc quidem aquis non convenit, sed hyperbolice melius exprimit miraculum. On the whole, the picture is not to be taken as a description of the historical circumstances connected with the taking of Babylon by Cyrus; neither, therefore, is the burning of the ponds to be referred to the fact that the bed of the Euphrates was made dry through diversion of the stream (Herodotus, i. 191); but we have here a poetic colouring given to the thought that all Babylon's means of offence and defence will fall into the power of the enemy and be destroyed by them. For (according to the reason assigned in Jeremiah 51:33 for what has been described) the Almighty God of Israel has decreed the destruction of Babylon. "The daughter of Babylon (i.e., not merely the city, but the kingdom of Babylon) is like a threshing-floor at the time when they tread it," i.e., stamp on it, make the ground into a threshing-floor by treading it hard.
(Note: "The threshing-floor is an open spot in the field, carefully levelled and cleared from stones, etc., that the grain may be spread out on it for threshing." - Paulsen, Ackerbau der Morgenl. S. 123. "A level spot is selected for the threshing-floors, which are then constructed near each other, of a circular form, perhaps fifty feet in diameter, merely by beating the earth hard." - Robinson's Pal. ii. 227.)
הדריכהּ might be the infinitive (Ewald, 238, d): it is simpler, however, to take it as a perfect, and supply the relative אשׁר. The meaning is, that Babylon is ripe for judgment. עוד מעט, "yet a little while" (i.e., soon), comes the time of harvest, so that the grain will be threshed, i.e., the judgment will be executed. The figure reminds us of Isaiah 21:10, cf. Joel 3:13, Micah 4:13, etc.

The passages - The passages over the river Euphrates, and all the other passages by which the Babylonians might make their escape, were guarded with soldiers. Reeds - On the border of the river Euphrates were vast quantities of great and tall reeds, which with the mud in which they stood, were as another wall to the city; but the Medes had burnt them so as the way was open.