Isa 31:4 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.
The LORD will let us know when danger comes. He will roar as a lion, as a lion of Judah after his cubs when men come to do them harm. Assyria was coming, would God's people seek Him, or would they trust in the might of Egypt? Is the LORD our help or the world, which is mightier? If we put our trust in the LORD we shall not perish. The LORD is not afraid of evil men, he will come to rescue those who trust in him.
Isa 31:5 As birds flying, so will the LORD of hosts defend Jerusalem; defending also he will deliver it; and passing over he will preserve it.
Three steps; the LORD, as a bird, perhaps an eagle in the air or an angel, the LORD will defend, he will deliver, and he will preserve. We know that calling on the name of God will bring angels to defend us. Next we need deliverance from sin by being in his Son Jesus, who will deliver us from the worlds power and the strongholds of satan as we submit all to him. As we trust in HIM and walk in His Spirit, we are preserved. Jesus our Savior will preserve us, sealing us with the Holy Spirit until this corruptible flesh becomes incorruptible.
Isa 31:6 Turn ye unto him from whom the children of Israel have deeply revolted.
Repent, turn to him again.
Isa 31:7 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.
Some things we must do. Cast off idolatry and sinful ways.
2 Cor 6:16 And what agreement hath the temple of God with idols? for ye are the temple of the living God; as God hath said, I will dwell in them, and walk in them; and I will be their God, and they shall be my people.
2 Cor 6:17 Wherefore come out from among them, and be ye separate, saith the Lord, and touch not the unclean thing; and I will receive you,
2 Tim 2:22 Flee also youthful lusts: but follow righteousness, faith, charity, peace, with them that call on the Lord out of a pure heart.
Isa 31:8 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.
Isa 31:9 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.
If they or we trust in the LORD, putting away sin and idolatry, then the enemy must flee the power of God. He is as a fire burning off the chaff from the wheat. The fire of God protects Zion and the intense fire is in his holy temple. We, in Christ Jesus are his holy temples. Jerusalem is the city of God, God will protect Jeruslaem. " For I will defend this city, to save it, for mine own sake, and for my servant David's sake."
The LORD defended Jerusalem as told in 2 Kings 19.
2 Ki 19:32 Therefore thus saith the LORD concerning the king of Assyria, He shall not come into this city, nor shoot an arrow there, nor come before it with shield, nor cast a bank against it.
2 Ki 19:33 By the way that he came, by the same shall he return, and shall not come into this city, saith the LORD.
2 Ki 19:34 For I will defend this city, to save it, for mine own sake, and for my servant David's sake.
2 Ki 19:35 And it came to pass that night, that the angel of the LORD went out, and smote in the camp of the Assyrians an hundred fourscore and five thousand: and when they arose early in the morning, behold, they were all dead corpses.
2 Ki 19:36 So Sennacherib king of Assyria departed, and went and returned, and dwelt at Nineveh.