"'Woe to the Assyrian, the rod of my anger, in whose hand is the club of my wrath!'" NIV translation
The "Assyrian" here is Sennacherib who was used by God to humble the people of Israel. The rod and the staff (club) were tools use by shepherds to guide and correct their sheep and this verse speaks to the fact that God was trying to get His people to see the error of their ways. The same is true for us as children of God in that the Holy Spirit guides and corrects us as needed to keep us in line with the will of God.
"'I send him against a godless nation, I dispatch him against a people who anger me, to seize loot and snatch plunder, and to trample them down like mud in the streets.'" NIV translation
God tells us exactly what He sent the Assyrians to do and it was simply to conquer the people of Israel. God did this to bring the people to repentance so that they might be saved. We all, at some point in our walk with the Lord, ask the question "Why is this happening to me?". The answer may simply be that God wants to humble us so that we depend on Him more and trust in Him more.
This can be true for us individually as well as together as a church or nation. A person or nation that has wandered a little too far from God's will for them can expect God to do a work like this in hopes of turning them back to Him. That is the loving correction of our Father in heaven.
"But this is not what he intends, this is not what he has in mind; his purpose is to destroy, to put an end to many nations." NIV translation
The Assyrians were not interested in what God would have them do but were only looking to extend their territory and glory. Sometimes, we can be like the Assyrians in that we want to do the will of God but we want to do it our way.
"'Are not my commanders all kings?' he says. 'Has not Calno fared like Carchemish? Is not Hamath like Arpad, and Samaria like Damascus?'" NIV translation
God shows us here the condition of the heart of the Assyrian leader and it is full of pride. He boasts of all of the lands that he has conquered and intends to do the same to the land of Judah. This is another reminder to us that God desires a humble heart and that pride is not of God. It was pride that caused the devil to want to replace God and be thrown out of heaven. It is this same sinful pride in the hearts of some leaders today that will lead to judgment just as it is here for the Assyrian. Even some Christian leaders take so much pride in their words that they try to replace the Word of God with their own.
You can listen to them preach and they share all kinds of their own words and ideas yet share little if any of the Word from the Bible. This is what the apostle Peter was talking about (2 Peter 2) and this will be judged as we see in Revelation chapter twenty.