>>16795713
Here’s a reasonable explanation from Pastor John MacArthur:
Notice carefully: “How art thou fallen from heaven, O Lucifer, son of the morning.” Lucifer means day star, son of the morning. To show you how elevated this creature was, you need only be reminded that in Revelation 22:16, it is said of Jesus Christ that He is the bright and morning star. When God wanted to speak of the brilliance and glory and magnificence of Christ, He calls Him the bright and morning star. Here, when the prophet refers to this created angel, he calls him also day star, son of the morning, and though he is not same as Christ, a similar expression is used to speak of the marvelous glory of this creature. So you understand this is a glorious creature. “How art thou fallen” is reminiscent of Luke 10:18 where Jesus said, “I beheld Satan as lightning fall from heaven.” “How art thou” – verse 12 – “cut down to the ground, who did weaken the people.”
https://www.gty.org/library/sermons-library/54-7/fighting-the-noble-war-part-1