Although the prophecy is directed toward the earthly king of Babylon (Isaiah 14:4), here it goes far beyond him (he could never fall from heaven) to the wicked spirit possessing his body and inspiring his actions. Just as Satan possessed and used the serpent's body in Eden, so he does here with Babylon's king.

Source:

KJV Defenders Study Bible, by Dr. Henry Morris, Ph.D.
Publisher: Thomas Nelson
Language: English
DEF 10 ISBN 0-529-10444-x
DEF 10-1 ISBN 0-529-10445-8