Babylon wasn’t a threat to the remaining kingdom of Judah at the time this was written. They inhabited modern Iraq, and were growing into a power worthy of confronting the Assyrians (with God’s help, raised up to be His instrument of judgment on the Assyrians), but we haven’t heard anything about them in the history we’ve read in Kings and Chronicles as of yet. They would rise to overthrow the Assyrians and take over and even enlarge the vast empire Assyria had built. When they did, their overthrow would be inconceivable. So the prophecy here is remarkable. Coming at a time before Babylon had even risen to power, in a way this prophecy foretells not only the end of Babylon, but what a great power it would become, as well.
The Day of the Lord is a day of unimaginable destruction. We know that we expect some of the catastrophes described here to happen in the end times in preparation for a new earth. So this prophecy is telling about that time still to come. An army coming from the ends of the heavens, all the heavenly lights darkened, world-wide punishment, earthquakes shaking the earth from its place – this speaks of the final destruction spoken of in Revelation. Yet this prophecy is about Babylon. The fall of that empire was not accompanied by heavenly wonders or earthquakes, but it was earth-shaking to the people who experienced it. The end of the Babylonian empire was so devastating it was like the end of the world. So the destruction foretold here applies to two distinct times: metaphorically describing the end of the Babylonian empire, and literally describing the end times yet to come. Relating the two gives us a greater understanding about the fall of Babylon.
Verses 14:12-15 describe Satan’s experience. I don’t know how scholars know that, but it is accepted by Bible scholars that this passage refers in part to Satan. The whole counsel of Scripture corroborates this account.
The peoples whose destruction was foretold in these chapters were people like us: they loved their children; they desired the good things life had to offer and worked to build a good life for themselves; they wanted security. Many of them doubtless felt secure in their walled cities, worshiping the gods that were supposed to protect them as they supposedly had protected their ancestors for centuries. As God revealed to His prophet Isaiah, they would be gone – not having faded away over time, but destroyed suddenly. These passages make dull reading for us because the people they talk about are so far gone that they have been long forgotten and are unknown to us. They were not dull reading to Isaiah’s first readers, because they knew these peoples well, had suffered destruction at their hands at times in their history, and ongoing threats from them. Our lack of knowledge of them is proof of God’s power over mankind, and His willingness and ability to judge.