Many times, God used evil men/nations as tools to carry out punishment of His people. Assyria had served that purpose against Israel. That, however, did not allow His “tools” to escape punishment. Assyria was about as evil and haughty as a nation could get. They boasted that it was through their own strength and gods that had allowed them to be superior in battle to the nations around them. Isaiah stated that God would destroy them like a wildfire that destroys everything in its path. They would attempt to take Judah as they had taken Israel, but God would protect the Judeans led by King Hezekiah.
Even though Assyria had captured Israel, there were scattered individuals that made up a remnant of Israel that had escaped. They, along with Judah would eventually be led by a new King who would come as a Rod from the stem of Jesse. That King was promised to David many years earlier as an unending kingdom. In retrospect, we know Him to be Jesus Christ and that His kingdom is His church.
The prophet used the picture of wild beasts and tame animals living together to describe the peace and harmony that would be present among the citizens of that new kingdom.
Isaiah penned two songs to be sung in praise to God. The first was a song of praise for His deliverance of them from the captivity of human hands. It expressed their trust in Him for their salvation. The second song called for all to recognize and exalt God for the deeds that He had done for His people. Christians should praise God for His deliverance from their sins.