I believe that this is from Robert's point of view. He kills Aurora and sees his lifework completed. That's why he gets slightly melancholy within the verses.
After "To take what is righteously mine" you can hear "Silverthorn"'s chorus melody played on the cello. I interpret it as Robert playing the melody ("Let me play a melody for you") with his Silverthorn, which kills Aurora.
I believe that this is from Robert's point of view. He kills Aurora and sees his lifework completed. That's why he gets slightly melancholy within the verses. After "To take what is righteously mine" you can hear "Silverthorn"'s chorus melody played on the cello. I interpret it as Robert playing the melody ("Let me play a melody for you") with his Silverthorn, which kills Aurora.