"The Lord will cause people to hear his majestic voice and will make them see his arm coming down with raging anger and consuming fire, with cloudburst, thunderstorm and hail." NIV translation
Why is God going to draw the nations to Jerusalem for a great battle before the Millennial Reign? We see that its purpose is to demonstrate once and for all the power of God Almighty. This is truly a "drop the mic" type of event where, once Jesus shows up, it is over!
"The voice of the Lord will shatter Assyria; with his rod he will strike them down. Every stroke the Lord lays on them with his punishing club will be to the music of timbrels and harps, as he fights them in battle with the blows of his arm." NIV translation
Now, Isaiah returns to talking about the situation that the residents of Jerusalem were facing at the time. He describes how God will take care of the Assyrian threat even as His people celebrate and worship with musical instruments.
"Topheth has long been prepared; it has been made ready for the king. Its fire pit has been made deep and wide, with an abundance of fire and wood; the breath of the Lord, like a stream of burning sulfur, sets it ablaze." NIV translation
Topheth is a place in the southeast end of the valley of the son of Hinnom which is south of Jerusalem. Basically it was the place where the trash was taken out of the city and burned so that there was constantly a fire burning and a stench that filled the air.
Although the fires do not burn there today (see picture at right), the place was a picture of the fiery pit of hell that awaits those who reject Jesus Christ.
Isaiah uses the picture of this place to reassure the people of Jerusalem that the Assyrians would be taken away from the city and the threat would be eliminated. The key was for them to wait on the Lord as he says that Topheth was "long prepared" for this time. The same thing goes for us as we face threats and trials in the world today.