31:1 Those who go down to Egypt for help are as good as dead, those who rely on war horses, and trust in Egypt’s many chariots and in their many, many horsemen. But they do not rely on the Holy One of Israel and do not seek help from the Lord. 

There were some rebellious leaders in King Hezekiah's political party who wanted to go down to Egypt to escape the Assyrian invasion. They trusted in Egyptian chariots more than they did in Jehovah. These rebellious leaders would die.

31:2 Yet he too is wise and he will bring disaster; he does not retract his decree. He will attack the wicked nation, and the nation that helps those who commit sin.

Those who go to Egypt will be committing a divine capital offensive sin against Jehovah. They will experience the sin-unto-death.

31:3 The Egyptians are mere humans, not God; their horses are made of flesh, not spirit. The Lord will strike with his hand; the one who helps will stumble and the one being helped will fall. Together they will perish.

These Egyptians were only human. Their horses were only made of flesh. They were not God. They would not be able to help Judah.

31:4 Indeed, this is what the Lord says to me: “The Lord will be like a growling lion, like a young lion growling over its prey. Though a whole group of shepherds gathers against it, it is not afraid of their shouts or intimidated by their yelling. In this same way the Lord who commands armies will descend to do battle on Mount Zion and on its hill.

Jehovah would attack Judah like a lion. Forty-six cities would be destroyed. The shepherds of Israel were the rebellious leaders of Israel. They would lead their sheep to danger and be torn to pieces. 

31:5 Just as birds hover over a nest, so the Lord who commands armies will protect Jerusalem. He will protect and deliver it; as he passes over he will rescue it.

Although Judah would be torn apart by the Lion of God, Jerusalem would be protected by a mother bird who was watching her nest. Jehovah was both the lion who would Judah, and the mother bird who would protect Jerusalem.

31:6 You Israelites! Return to the one against whom you have so blatantly rebelled!

Isaiah called on Israel to turn back to God.

31:7 For at that time everyone will get rid of the silver and gold idols your hands sinfully made.

During the Millennial Kingdom, Israel will finally throw her idols away.

31:8 Assyria will fall by a sword, but not one human-made; a sword not made by humankind will destroy them. They will run away from this sword and their young men will be forced to do hard labor.

Assyria would fall by supernatural means.

31:9 They will surrender their stronghold because of fear; their officers will be afraid of the Lord’s battle flag.” This is what the Lord says— the one whose fire is in Zion, whose firepot is in Jerusalem.

 Assyria would not be able to stop Jerusalem’s burnt offerings to Jehovah, because God would supernaturally destroy them.