And the brooks of defence shall be emptied and dried up. [1] What he adds about fortifications is to the same purpose with what he had stated immediately before. He alludes to the embankments, which not only restrained the overflowing of the Nile, but protected the whole country; as if he had said that the embankments will not be needed, because the Nile will be dried up. Now, it is certain that the Nile was not laid dry, and yet the Prophet did not foretell what was not accomplished. We must therefore call to remembrance what we have already said, that on account of our stupidity those calamities are represented to us in a lively manner, which places them as it were before our eyes; for we need to have a representation made to us which is fitted to impress our minds, and to arouse us to consider the judgments of God, which otherwise we despise. We ought to observe the haughtiness of the Egyptians, whose resources were so various and abundant, and who thought that it was impossible for them to be overtaken by such a calamity.

Footnotes

1 - "Embanked canals. Rivi aggerum, as the Vulgate has it. The canals by which the waters of the Nile were distributed were fortified by mounds or banks. mtsvr, (matzOr,) which word Rosenmüller vainly endeavors to shew to be another name for Egypt or Mizraim." -- Stock.

And they shall turn the rivers far away - (האזיּחוּ he'ezenı̂ychû), probably from זנח zânach, "to have an offensive smell; to be rancid, or putrid." The word in this form occurs nowhere else. It is in the Hiphil conjugation, and is probably a form made from a mixture with the Chaldee. The sense is not doubtful. It means 'the rivers shall become putrid - or have an offensive smell;' that is, shall become stagnant, and send forth unwholesome "miasmata" producing sickness, as stagnant waters often do. The Vulgate renders it, 'And the rivers shall fail.' The Septuagint, 'And the Egyptians shall drink the waters from the sea, but the river shall fail, and be dried up, and the rivers shall fail, and the streams (διὼρυχες diōruches) of the river, and all the assembling (συναγωγή sunagōgē) waters shall be dried up.'
And the brooks of defense - Hebrew, 'The rivers of מצור mâtsôr. The word מצור mâtsôr often means "straitness, affliction;" then a siege, a wall, a bulwark, a fortification. But, probably, it here means "Egypt," or the same as מצרים mı̂tserayı̂m (compare Isaiah 37:25; 2-Kings 18:24; Mark 7:12). Perhaps the Hebrews may have thought of Egypt as a strongly fortified place, and thus have given the name to it; or possibly this may have been a modification of the name "Mitsraim."
The reeds and flags - Which grew on the banks of the Nile - the papyrus, etc. (see the note at Isaiah 18:2)

Shall turn the rivers far away "Shall become putrid" - האזניחו heeznichu. This sense of the word, which Simonis gives in his Lexicon, from the meaning of it in Arabic, suits the place much better than any other interpretation hitherto given; and that the word in Hebrew had some such signification, is probable from 2-Chronicles 29:19, where the Vulgate renders it by polluit, polluted, and the Targum, by profaned, and made abominable, which the context in that place seems plainly to require. The form of the verb here is very irregular; and the rabbins and grammarians seem to give no probable account of it.

And they shall turn the (f) rivers far away; [and] the brooks of defence shall be emptied and dried up: the reeds and flags shall wither.
(f) For the Nile ran into the sea by seven streams, as though they were many rivers.

And they shall turn the rivers far away,.... The river Nile, called "rivers", the plural for the singular, because of the abundance of water in it; or its seven streams, with other rivulets, derived from it. Some make the "they" here to refer to the kings of Egypt, and interpret the words of some projects of theirs, by which the course of the river was turned to great disadvantage; particularly they understand it of the twelve tyrants that reigned after Sethon, to whom they ascribe the digging of the vast lake of Moeris, the two pyramids built in the midst of it, and a labyrinth near it, though only the labyrinth was made by them (b); and as for the lake, it was made by Moeris, a king of Egypt, from whom it had its name, some hundred years before; and, besides, was of service, and not disservice, to the Nile; for it received its waters when it overflowed too much, and it furnished it with water by an outlet when it failed: rather therefore this passage may be illustrated by the attempt which Necus, the son of Psammiticus, whom the Scripture calls Pharaohnecho, made, to join the Nile and the Red Sea together, by making a canal from the one to the other; in which work he lost a hundred and twenty thousand men, and desisted from it without finishing it (c); but it is thought hereby the river was greatly weakened:
and the brooks of defence shall be emptied and dried up; as the river of Nile and its streams were the defence of the land of Egypt, as well as made for the fruitfulness of it, for these must make it less accessible to a foreign enemy; and besides, here lay their shipping, which were their protection; and moreover, from hence brooks and courses of water might be derived and carried about their fortified cities, which added to the strength of them. The Targum renders it deep brooks or rivers; and Kimchi interprets it the brooks of Egypt, taking Matzor to signify Egypt, a word in sound near to Mitzraim, the common word used for Egypt. It looks, by this and other expressions in the context, as if more were designed than the above instance or instances will account for:
the reeds and flags shall wither; which grew in the brooks, and near them; and therefore much more the grass and corn, and other trees, which were at a distance; besides, these are mentioned, bemuse of the great usefulness they were of; for of these they made ships, barks, and boats, and mats for bedding, and nets fishing; as also paper to write on, as follows, and which was a staple commodity with them; See Gill on Isaiah 18:2.
(b) Herodot. l. 2. c. 148, 149. (c) Ib. c. 158.

they shall turn the rivers--rather, "the streams shall become putrid"; that is, the artificial streams made for irrigation shall become stagnant and offensive when the waters fail [MAURER]. HORSLEY, with the Septuagint, translates, "And waters from the sea shall be drunk"; by the failure of the river water they shall be reduced to sea water.
brooks of defence--rather, "canals of Egypt"; "canals," literally, "Niles," Nile canals, the plural of the Egyptian term for the great river. The same Hebrew word, Matzor, whence comes Mitzraim, expresses Egypt, and a place of "defense." HORSLEY, as English Version translates it, "embanked canals,"
reeds . . . flags--the papyrus. "Reed and rush"; utter withering.

Rivers - The rivers (those rivulets by which the waters of Nile were distributed into several parts of the land) shall be turned far away, as they must needs be, when the river which fed them was dried up. Brooks - The several branches of the river Nile, which were a great defence to Egypt. Reeds - Which were useful to them for making their boats. Whither - As they commonly do for want of water.