 Lucifer was a covering Cherub .  He was beautiful and musical. 
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God gave man something Lucifer never had - Authority . God gave Dominion over the earth to man.  
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 Lucifer saw what God had given man and coveted it.  God was making mankind not just His Creation but He was making them His Children .  This was a place of elevation Lucifer could never attain.  
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 Lucifer`s lust for the Authority that God had given man caused him to deceive Eve and then Adam into taking his advice rather than God`s.  He became ruler of this world by man`s abdication and deference to him.  
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 Lucifer became Satan .