v1: Vain is the help of man! Israel and probably Judah also had sought Egypt’s help (30.1-5; 36.6). They looked to the multitudes and the strength of chariots and horsemen, but failed to look to the Lord God, whose strength far exceeds. Egypt’s own horses and chariots were destroyed in the crossing of the Red Sea (Ex 14-15).
v2: The Lord is wise, seeing our folly. His wisdom is consistent with His faithfulness to His own,, and with His holiness, for He will punish the evildoers.
v3: The Egyptians, needless to say, are not God; they are flesh not spirit. The helper and the helped fall together; the blind leading the blind, and both falling into the ditch.
v4-5: The Lord is the lion, unmoved by the multitude of shepherds arrayed against Him. He fights for His people, and for Zion, His city. The Lord is also the bird, flying over those He loves. The Lord’s jealousy; we can have total confidence in Him; He will shield, deliver, 'pass over,' and rescue. The verses bring together striking paradoxical characteristics of God – lion and bird; shield and deliver; pass over and rescue; some see this as bringing together typically make and female characteristics.
v6: Recognise past rebellion, and repent of it. We can turn back to Him, for He is faithful and true.
v7: See 30.22; the people put away their idolatry. This is important; the Lord stayed loyal to His people, although they were disloyal to Him.
v8-9: Defeat for Assyria, 30.31-32; their defeat was ordained by the Lord God, the Holy One of Israel. At the time of Isaiah’s writing, Assyria was the dominant power in the Middle East; their fall was hard to imagine. In the longer term, Assyria was representative of the Gentile nations who attack and oppress Israel. See 37.36-38, where this specific prophecy is fulfilled.
Assyria found God’s furnace in Jerusalem; the place of judgment. But God’s people already knew this; at the centre of His people there was judgment for sins, and the demonstration of divine justice. See 1 Pet 4.17. God has indeed chosen His people for His glory – is it any surprise that He works to purge us?