Elder Bruce R. McConkie explains the title ‘son of the morning’:
“…this name-title of Satan indicates he was one of the early born spirit children of the Father. Always used in association with the name Lucifer, son of the morning also apparently signifies son of light or son of prominence, meaning that Satan held a position of power and authority in [the] pre-existence.” (Mormon Doctrine, p. 744)
Lucifer fell from heaven for rebelling against God the Father and His plan of salvation. ’He was cast out into the earth, and his angels were cast out with him’ (Rev 12:9). ‘And his tail drew the third part of the stars of heaven’ (Rev 12:4).
In the very next phrase, ’Art thou cut down to the ground, which did weaken the nations’, we understand that Isaiah is now referring to the time when Satan is cast out at the beginning of the Millennium. When Satan is finally stripped of all power, the people will look upon him and ’say: Is this the man that made the earth to tremble, that did shake kingdoms?’ (v. 16) His power over the wicked of the world and the glory and majesty of the great whore will be destroyed just as the glory of the king of Babylon came to naught:
’How much she hath glorified herself, and lived deliciously, so much torment and sorrow give her: for she saith in her heart, I sit a queen, and am no widow, and shall see no sorrow.
Therefore shall her plagues come in one day, death, and mourning, and famine; and she shall be utterly burned with fire: for strong is the Lord God who judgeth her.’ (Rev 18:7-8)