Michael Fishbane, Biblical Myth and Rabbinic Mythmaking (New York: Oxford University Press, 2003) 74-75.
Fishbane states the following about Isaiah 14:4-21's description of Lucifer, who tried to ascend to heaven and be like the Most High, only to be brought down to Sheol (the Underworld):
Other cases of metamorphosis report myths of the punishment or descent of heavenly beings into earthly existence. The cause of the demotion is not always indicated. For example, in Isa. 14:4-21 the king of Babylon is rebuked for his hubris and divine pretensions, and mockingly identified with Helel ben Sha[ch]ar, a luminous day star who was cast out of heaven. It is not stated just what that astral deity did to be brought down; but one may perhaps reconstruct the underlying myth from the diatribe in which the king is ironically identified with the god. 'How you have fallen (nafalta) Helel ben Sha[ch]ar'---you who 'thought ('amarta) in your heart, "I shall ascend ('e'eleh) heaven, raise my throne above the stars of El, and sit in the mountain of (the divine) assembly in the recesses of Saphon; I shall ascend upon a cloud and be like Elyon"!' (vv. 12-14). For this rebuke it may be assumed that the god fell because of his pretension for high estate in the pantheon. That such a mythic structure existed in confirmed in Canaanite sources from a halk-millennium earlier. Here too we read of an astral deity (named Athar) who 'ascended (y'l)' beyond his station to the recesses of Saphon; and when he sat upon the throne of Alyan Ba'al he proved inadequate and descended to rule the underworld. The theme of punishment is not found here, but enough of a resemblance exists to conform that the political diatribe in Isa. 14:4-21 has reworked the myth of a pretensious god who undergoes a change of status and leaves the heavenly hierarchy.
The story of the fall of Lucifer was often a key theme in my own religious background. I remember when I was little, and I saw a cartoon about Satan on Bugs Bunny. (I think he may have been judging Yosemite Sam.) I asked my mom who the devil was, and she told me to ask my father. And so I did so that night, and my dad told me the enthralling story about how an angel named Lucifer tried to lead other angels in a revolt against God, only to be cast out of heaven. Lucifer then became Satan, my dad said. Whenever we watched the World Tomorrow TV show and the topic was Satan, the announcer would cite Isaiah 14 as the story of the fall of Lucifer.
Seventh-Day Adventism was much the same way. I don't know how many times I heard the story of the fall of Lucifer, but it was a lot, I can tell you that! The Adventist speakers often said that God didn't destroy Lucifer because that would confirm Lucifer's lie that God is mean and unjust, a lie that (for Adventists) God has been trying to refute from creation until now.
When I checked out Isaiah 14 for myself, I learned that it's about the king of Babylon, which wasn't exactly highlighted (or even mentioned) whenever I heard Armstrongites or Adventist teachers expound the passage. For them, it was about the origin of Satan, period! And some Christians have asserted that Isaiah 14 has nothing to do with Satan because it's about the king of Babylon, as this passage from John Calvin's Isaiah commentary demonstrates (see here):
The exposition of this passage, which some have given, as if it referred to Satan, has arisen from ignorance; for the context plainly shows that these statements must be understood in reference to the king of the Babylonians. But when passages of Scripture are taken up at random, and no attention is paid to the context, we need not wonder that mistakes of this kind frequently arise. Yet it was an instance of very gross ignorance, to imagine that Lucifer was the king of devils, and that the Prophet gave him this name. But as these inventions have no probability whatever, let us pass them as useless fables.
But I liked something that Adventist scholar Samuele Bacchiocchi said about Isaiah 14: it's about the king of Babylon, but it's also about Satan, for Isaiah is likening the king of Babylon to Satan. Both tried to elevate themselves to the status of God and were humiliated as a result.
As a side issue, I wonder something: What does the Bible say about Satan's exact location after he was cast out of heaven? I was taught that he roams the earth or is in outer space, below the highest heaven. Job 1:7 presents Satan in heaven saying to God that he'd just been roaming to and fro about the earth, and I Peter 5:8 states that he roams about as a roaring lion, seeking whom he may devour. Jesus says in Luke 10:18 that he saw Satan fall like lightning from heaven, which many Christians apply to the fall of Lucifer before the creation of the heavens and earth, and many scholars relate to the ministry of Jesus, who bound Satan by bringing people to repentance, healing their diseases, and casting out demons. So is Satan here on earth? Revelation 12:10 seems to present Satan's expulsion from heaven as future: right now, he's in heaven before the throne of God accusing the Christians, but there will come a time when he'll be cast down to earth.
But Isaiah 14 says that Lucifer is in Sheol, the underworld. People at my elementary school pointed to the ground as the location of Satan, assuming that he was under the earth in a fiery place called hell. My religious background dismissed that idea as popular mythology, asserting instead that Satan was active on planet earth. But, if Isaiah 14 is indeed about Satan, then one biblical tradition says he's underground, meaning popular mythology didn't come out of the clear blue sky.
At the same time, Isaiah 14:16 says Lucifer will be cast down to Sheol. Maybe he's not in Sheol right now but is still trying to take the place of God and be like the Most High. Perhaps his "casting down" to the Underworld will occur in the future.
But is Isaiah 14 really about Satan? At DePauw, a philosophy professor of mine said that the story of the fall of Lucifer is not in the Bible but is from John Milton's Paradise Lost. Yet, she pointed out that it's become a widely-accepted story among Christians! But people long before Milton associated the fallen Lucifer of Isaiah 14 with Satan (see here, here, and here).
When I asked my Hebrew Bible professor at DePauw about Isaiah 14, he replied the same way Fishbane addresses the issue: Isaiah 14 is about an ancient Near Eastern god who tried to overthrow El and got cast to the underworld. Actually, if my memory is correct, my professor said that tales about an ancient battle between the gods were common in the ancient Near East, and we do see one such example in the Babylonian Enuma Elish.
As Fishbane states, the story of a god trying to enroach his way into a higher god's throne was common in some way, shape, or form and for quite some time in the ancient Near East. Remember that not all of the writers of the Hebrew Bible were adverse to the existence of other gods besides YHWH (see Deuteronomy 32:8; Psalm 82:1), so the author of Isaiah 14 may have accepted an ancient Near Eastern story about an astral deity named Helel ben Shachar who sought to be like the top god, the Canaanite deity El (whom Israelite religion identified with YHWH). And he compared the Babylonian king with this Helel. He apparently didn't see a need to explain who Helel was, so he probably assumed that most of his audience knew about him, presumably through the ancient Near Eastern story.
But, even if Isaiah 14 originally may not have viewed Helel ben Shachar as the Lucifer/Satan of our understanding, can we still apply Isaiah 14 to Satan? The New Testament has the theme of Satan being cast out of heaven, and I wouldn't be surprised if it got that idea from Isaiah 14! Maybe the story of the astral deity Helel who tried to be equal with God is a piece of a larger puzzle of who Satan is. And, somehow, that sort of story was in the minds of people who lived before the earliest books of the Bible were even written!