Gandalf did not have his staff to use against the Balrog, so he had to use the sword as a conductor of his magic. Also, his sword , Glamdring, was forged for the High King of the Noldor, Turgon Lord of Gondolin, who used this sword to fight Balrogs.
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He came unto the timeless halls where shining fall the countless years and endless reigns the Elder King in Ilmarin on Mountain sheer
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