In these four verses we get an opportunity to see how the mind of Isaiah works. In verses 4 and 5 Isaiah is looking at the great city of Babylon. The whole city is surrounded by walls 336 feet high and 136 feet wide. On the top of the wall houses are built on both sides, and a street between the houses wide enough for three chariots to drive abreast.
When Cyrus and his tens of thousands surround this wall the Babylonians watched curiously as thousands of the soldiers dig a trench around the wall. But the king of Babylon, named Belshazzar, was not worried. He was having a great feast in his palace when unexpectedly a hand came out and wrote on the wall. No one could translate the writing so they sent for the aged Daniel who was still alive and after interpreting the writing he told Belshazzar that the great city was about to be conquered, and then he went his way.
It was about this time that Cyrus and his soldiers diverted the river that ran through the city into the ditch they had dug and Cyrus had his vast army march along the old river bed that passed beneath the walls. Immediately the conquest of Babylon began. That night King Belshazzar was murdered and by morning Cyrus was in charge of the whole city.
As Isaiah watched in vision what would happen to ancient Babylon his mind suddenly switched to his vision of the destruction of the wicked Gentile Babylon of the last days. This time it is not just the destruction of a city but of a whole civilization. Suddenly, and without telling us that his eyes are looking at the cataclysmic destruction of the wicked just before the Second Coming, he begins describing what he is seeing. This narrative about the latter days will last until verse 16, then he will switch back to the destruction of ancient Babylon for the rest of the chapter.
Isaiah must be read very carefully so that you know what he is seeing and describing. Notice that in verse 6 he says "the day of the Lord is at hand." Here he has switched from his day to our day. He says the destruction of the wicked in the latter days will also be by the hand of the Almighty. In verse 7 he says the destruction will be so overwhelming that men's hearts will fail them for fear.