Complex sentence: Realizing he is close to following in his father's footsteps, Luke refuses the Emperor's command to kill Vader and take his place, and so the Emperor, enraged, unleashes a torrent of Force lightning upon Luke.
Split into simpler sentences: Realizing he is close to following in his father's footsteps, Luke refuses the Emperor's command to kill Vader and take his place. Enraged, the Emperor unleashes a torrent of Force lightning upon Luke.