What does Isaiah 10:5 mean?
Israel has been receiving a warning about the coming judgement of the Lord (Isaiah 10:3–4). The Assyrian army was powerful, brutal, and greatly feared all over the Near East. Assyrian kings were ambitious to take possession of all the nations within their reach. Now, the Lord makes clear that Assyria is not His chosen people. Despite Isaiah's prophecy that Assyria will succeed in conquering Israel and bringing destruction to Judah, he proclaims "woe" upon them, as well. After they have served God's purpose as an instrument of punishment, the Assyrians, too, will be punished.For now, the Lord calls them the rod of His anger. Their weapons are the extension of His fury. Two things leap out from these statements. First, the power of the nations are nothing compared to the Lord. He raises them up and tears them down for His own purposes. While Judah quakes at the coming of Assyria, they should be trembling at the power of the Lord. Instead of trying to make alliances with Assyria's king, as Judah's King Ahaz did, the people of Judah should be trying to renew their full dependence on the Lord (2 Kings 16:7–9).
The other thing made obvious by Isaiah's quotation from the Lord here is that God is more than annoyed with Israel. He is furious. He is livid with rage. He will wield the destructive power of the Assyrian empire against Israel and Judah due to their ongoing unfaithfulness to Him.