1 Woe to them that go down to Egypt for help; and stay on horses, and trust in chariots, because they are many; and in horsemen, because they are very strong; but they look not unto the Holy One of Israel, neither seek the LORD! 2 Yet he also is wise, and will bring evil, and will not call back his words: but will arise against the house of the evildoers, and against the help of them that work iniquity. 3 Now the Egyptians are men, and not God; and their horses flesh, and not spirit. When the LORD shall stretch out his hand, both he that helpeth shall fall, and he that is holpen shall fall down, and they all shall fail together. 4 For thus hath the LORD spoken unto me, Like as the lion and the young lion roaring on his prey, when a multitude of shepherds is called forth against him, he will not be afraid of their voice, nor abase himself for the noise of them: so shall the LORD of hosts come down to fight for mount Zion, and for the hill thereof. 5 As birds flying, so will the LORD of hosts defend Jerusalem; defending also he will deliver it; and passing over he will preserve it. 6 Turn ye unto him from whom the children of Israel have deeply revolted. 7 For in that day every man shall cast away his idols of silver, and his idols of gold, which your own hands have made unto you for a sin. 8 Then shall the Assyrian fall with the sword, not of a mighty man; and the sword, not of a mean man, shall devour him: but he shall flee from the sword, and his young men shall be discomfited. 9 And he shall pass over to his strong hold for fear, and his princes shall be afraid of the ensign, saith the LORD, whose fire is in Zion, and his furnace in Jerusalem.
[AD 397] Ambrose of Milan on Isaiah 31:1
Let our course take us to regions above, because it is better to ascend. Finally, as was read today, “Woe to them that go down to Egypt.” Surely it is not wrong to go to Egypt, but to change to the ways of the Egyptians, to change to the violence of their treachery and to the ugliness of their wantonness—this is wrong. He that changes in this way descends, and one who descends falls. Let us keep away, then, from the Egyptian who is a man, but [let us] not [keep away] from God. Even the king of Egypt himself fell under the dominion of his own vices and in comparison with him Moses was accounted a god, ruling over kingdoms and subjecting powers to himself. So we read that it was said to Moses: “I shall make you a god to Pharaoh.”

[AD 420] Jerome on Isaiah 31:1-3
(Chapter 31, verses 1 onwards) Woe to those who go down to Egypt for help, who rely on horses, who trust in the multitude of their chariots and in the great strength of their horsemen, but do not look to the Holy One of Israel, or seek help from the Lord. Yet he too is wise and can bring disaster; he does not take back his words. He will rise up against the wicked nation, against those who help evildoers. Egypt is a man and not a God: and their horses are flesh, not spirit: and the Lord shall lay his hand upon them that help, and the helper shall fall down, and he that is helped shall fall, and they shall all be consumed together. After the burden of the beasts of the south, and the treasures of their riches for the people of Egypt shall exhaust their aid, which shall be of no profit to them, but for a shame and a reproach. Look now towards the land of the north wherein is the king of Babylon: where is now the old king of Assyria? Where are their gods in whom they trusted? Who is the king of Hamath, and of Arphad, and of the city of Sepharvaim, of Ana, and of Ava? And as for Hamath it had the beginning from Samaria: but Samaria and Jerusalem shall receive the reward of their trusting in him. For their God is with them and they glory in their king. With their horses and chariots they shall go up, and with their horsemen and their troops they shall come down, and they shall cover the land as a sea. And they shall pass through it unharmed: and they shall fall into captivity. And they that shall be gathered together against them, shall be confounded: and all the beasts of the field, and all the fowls of the air, and the birds of the sea shall be gathered together upon them: and the Lord will for them carry on a war, and will afflict them. Their strength shall be consumed with famine: and their birds shall be devoured with a burning heat, and with most grievous destruction: because they have despised the words of the Lord, and have depised the counsel of the holy one of Israel. And this is both the present and the past, where it is prescribed that the Jews should not go down to Egypt; here, because they have despised the Lord's command, it is prophesied that they will go down, and that both Israel and the Egyptians, both the fugitives and the helpers, will be slain by King Nebuchadnezzar of Babylon. Jeremiah speaks at length about this (Jeremiah 42). Woe therefore to those who go down to Egypt and despise the Lord's command in fear of the Chaldeans, hoping in idolaters who boast of having the worship of God, and relying on the help of horses, not knowing the scripture: A deceitful horse brings salvation (Psalm 32:17); and they have confidence in chariots, horses, and riders, not remembering that song: He has cast chariots and their riders into the sea (Exodus 15:1). And they did not trust in the Holy One of Israel, who promised them help through Jeremiah for those who remained in the land of Judah. And they did not seek the Lord; not that they did not seek, but that they disregarded the words of the one they sought. And this is also said of the wicked priests: They devour my people and do not call upon the Lord (Psalm 52:5,6). But the wise one, that is, the Lord, brought evil upon them, and the worst, namely Nebuchadnezzar, or rather, he brought about evil as a consequence, not as a personal intention; and he did not take away his words that he had spoken through the prophets. How will it rise up against the tribe of Judah, the house of the wicked, and against the help of the Egyptians, who work iniquity? For Egypt, or the Egyptians as the Septuagint translated, is a man and not God; and their horses are flesh and not spirit. Therefore, it is written in Jeremiah: Cursed is the man who puts his trust in man and has made flesh his strength, and his heart has turned away from the Lord. And he will be like a shrub in the desert, and shall not see when good comes (Jeremiah 17:5-6). And in another place it is written: The salvation of man is in vain (Ps. 59:13), or, as is better understood in the Hebrew, in man. And when the Lord stretches out His hand to punish, or turns away, under the metaphor of a charioteer, and loosens the reins of the horses that are running, the Egyptian helper will fall, and the help that was given to Israel. Indeed, we can understand this about those who, in times of persecution, tribulation, and distress, do not trust in the Lord, but in the help of the Egyptians, that is, of worldly men; not knowing that Abraham was in danger in Egypt, and that the people of God served in that region of mud and bricks, which is spiritually called the iron furnace. Wherefore also in the Apocalypse of John it is read: The place in which the Lord was crucified is spiritually called Sodom and Egypt (Al. Egyptian) (Apoc. XI, 8).

[AD 420] Jerome on Isaiah 31:4-5
(Verses 4, 5.) For thus says the Lord to me: Just as when a lion roars, and a lion cub over its prey, when a multitude of shepherds come against it, it will not be afraid of their voices, nor terrified by their numbers; so the Lord of hosts will come down to fight upon Mount Zion and its hill. Like birds hovering, so the Lord of hosts will protect Jerusalem, protecting and delivering, passing over and saving. In manifestis unam ponimus editionem, maxime ubi nulla diversitas sensuum est. Caesis in Aegypto Israelitis et Aegyptiis, in quorum auxilio confidebant, revertentur (( Al. revertuntur)) in Jerusalem, Cyro regnante, captivi. Et per duas similitudines, Domini, qui se fore adjutorem promiserat, fortitudo monstratur. Sicut leo et catulus leonis esuriens, si cernat ovium gregem, nulla pastorum voce terretur, et multitudinem eorum conscius virium suarum despicit: sic Dominus exercituum praeliabitur, non contra montem Sion et collem ejus, super montem Sion contra adversarios illius. Let us give another comparison: Just as birds defend their offspring by flying over their nests, and whether they see a snake or a human, the birds and others approach their chicks, forgetting their weakness, they fight with their beaks and claws, and with a chattering voice they express their anguish: so the Lord will protect Jerusalem and deliver it by passing over, and He will save it. For 'passing over' in Hebrew is 'Phase', and it is translated as 'ὑπερβαίνων' by the interpreters, apart from the Septuagint. From which it is clear that Pascha, that is, the Lord's Passover, does not signify His passion, but His passage. Moreover, that the Lord acted as the protector in the likeness of birds over Jerusalem, He Himself testifies in the Gospel: 'Jerusalem, Jerusalem, you who kill the prophets and stone those sent to you' (Matt. XXIII, 37): how often have I desired to gather your children together, as a hen gathers her chicks under her wings, and you were not willing? And in Deuteronomy it is said of the Lord: He spread his wings and took them, and carried them on his shoulders (Deut. XXXII, 11).

[AD 420] Jerome on Isaiah 31:6-9
(Verse 6 onwards) Return, as you have deeply strayed, O children of Israel. For on that day a man will cast away the idols of his silver and the idols of his gold, which your own hands have made for yourselves to sin. And Assur will fall by the sword, not of a man; and a sword, not of a human, will devour him. He will flee not from the face of the sword, and his young men will become forced labor. His strength will pass away in terror, and his fleeing princes will be filled with fear, says the Lord, whose fire is in Zion and whose furnace is in Jerusalem. LXX: Return, O children of Israel, as you have gone deep into sin. For on that day every man will throw away the idols of his silver and the idols of his gold that your own hands have made for your own sins. And Assyria will fall by the sword, not of a man, and a sword, not of a human, will devour him; he will flee, but not from the face of the sword; his young men will be defeated; they will be surrounded like a wall, and they will be conquered; but whoever flees will be captured. Thus says the Lord: Blessed is he who has offspring in Zion and who has a household in Jerusalem. While the Lord fights against his adversaries on Mount Zion and protects it like a rampart, O children of Israel, turn back! As Symmachus translated it: Repent, you who have strayed from the Lord due to deep counsel and sin. For if you do this, casting aside the golden and silver idols that have been a cause of sin for you, because of which your city was captured, Assyria will fall, from whose fear you now flee, not by the sword of men or the strength of an army, but by the power of God. But it signifies that an angel, by whom 185,000 Assyrians were destroyed in one night. Also, the Assyrian king himself will not flee from the sword of men, but from the wrath of God, so that his young and strong men will become tributaries to the Medes, of whom it is said above, in opposition to Babylon: Behold, I will raise up the Medes against you. And the might of Assyria will pass by with the terror of the Lord, and all its princes will tremble. For the Lord has spoken and promised, and what He has said, He has done: and He who has fire in Zion and a furnace in Jerusalem, so that He may consume His adversaries like straw and wood coming out of Jerusalem. Another thing that is said: On that day, a man will throw away his idols of silver and the rest, it is interpreted in such a way that it testifies that after the return from the Babylonian captivity until the coming of Christ, the children of Israel never worshiped idols. Assyria is also signified in the present place, not by an angel, but by the Medes, because it was the most ancient and once powerful kingdom, which was destroyed after offending the Lord, and served the conquerors. The Nazarenes understand this place thus: O children of Israel, who denied the Son of God with wicked counsel, return to Him and His Apostles. For if you do this, you will cast away all the idols that were previously a sin for you, and the devil will fall to you, not by your strength, but by the mercy of God; and its young men who once fought for it will be subjects of the Church, and all its strength and rock will be passed to it; even the philosophers and every perverse doctrine will turn their backs to the sign of the cross. For the opinion of the Lord is that this should be done: whose fire or light is in Zion and his furnace in Jerusalem. Fire and light are written in Hebrew with the same letters Aleph, Vau, Res; if it is read as Ur, it means fire: if Or, it means light. This is said because for the fire, which Symmachus alone interprets, Aquila and Theodotion translate it as light. But I do not know what is meant by what is read in the Septuagint: They will be surrounded like a wall by rock, and they will be conquered: but whoever flees will be captured. Unless perhaps we can say this, that the young men of the Assyrian king who are to be conquered and captured, are surrounded like a rock, that is, by the strength of the Lord, just as a city is surrounded by a wall. Furthermore, what follows: Blessed is the one who has offspring in Zion, and domestic servants in Jerusalem, we can interpret it in such a way as to say that it agrees with the meaning of this place, that the divine word exhorts those who are fleeing to Egypt to return to Jerusalem and to bear children. To whom such great blessedness is promised, that it may be defended and protected by the help of the Lord. And in another place it is written about it: The glory of this last house shall be greater than the glory of the former (Haggai 2:10). Which can also be referred to the Church, the vision of peace and the watchtower, of which it is written: Glorious things are spoken of you, O city of God (Psalm 87:2). And elsewhere: The streams of the river make glad the city of God (Psalm 46:3). For in it there is fire and a furnace that shall devour the sinners, and shall consume the wood, hay, and stubble; or it is a light and an oven, that the brightness of the righteous, and the punishment of the wicked, may be shown.

[AD 420] Jerome on Isaiah 31:6
In place of the last clause [“But you have played the harlot with many lovers; yet return again to me, says the Lord.”] the true Hebrew text (which is not preserved in the Greek and Latin versions) gives the following: “you have forsaken me, yet return, and I will receive you, says the Lord.” Isaiah also speaking in the same sense uses almost the same words: “Return,” he cries, “O children of Israel, you who devise a deep and sinful counsel. Return to me, and I will redeem you. I am God, and there is no God else beside me; a just God and a Savior; there is nothing beside me. Look to me, and be saved, all the ends of the earth.” Remember this and show yourselves men: bring it again to mind, O you transgressors. Return in heart and remember the former things of old: for I am God and there is none else.”

[AD 604] Gregory the Dialogist on Isaiah 31:9
Of this love that is begun here to be perfected from the sight of the Lord in the eternal kingdom Isaiah rightly speaks, saying, “The Lord lives, whose fire is in Zion, and his furnace in Jerusalem.” It is, however, greater to be a furnace than a fire because a fire can also be small, but a larger flame is kindled in a furnace. Zion truly is said to be speculation but Jerusalem the vision of peace. Truly we sometimes catch a glimpse of our peace here in order there later to see it fully. Therefore through the Lord’s love the fire is in Zion and his furnace in Jerusalem because here we burn in some measure with the flames of his love when we glimpse him, but there we shall burn totally when we shall fully see him whom we love.

[AD 735] Bede on Isaiah 31:9
If the breads of the furnace that were baked in secret signify the interior devotion of the mind of the faithful confirmed by the fire of charity, breads which were also commanded by the law to be offered in the sacrifice of the Lord, it is most fitting that the hearts which were made to burn constantly with the flame of intimate love and virtue and to beget words are symbolized through the furnaces in which the same breads were baked. The prophet spoke beautifully about these things when he referred to “the Lord whose fire is in Zion and whose furnace is in Jerusalem.” It is also written: “Did our hearts not burn within us when he spoke along the way and opened the Scriptures to us?”

[AD 749] John Damascene on Isaiah 31:9
The prescription of the law must be taken in the more spiritual sense. For there is a spiritual seed which through charity and the fear of God is conceived in the womb of the soul, which in turn travails and brings forth the spirit of salvation. It is in this sense that the passage is to be taken which reads, “Blessed is he who has seed in Zion and kindred in Jerusalem.” What, indeed! Even though one is a fornicator, a drunkard or an idolater, will he be blessed, provided only that he has seed in Zion and kindred in Jerusalem? No one in his right mind would say that.