Wielding the Flame of Anor

[Nilpaurion Felagund]

Yes. I did. No denying that.

I agree with HerenIstarion on this:

Gandalf on the bridge was trying to avoid battle. His utterances were at the same time a war boast, and a warning, and a hope beyonf hope that Balrog would just leave them alone.

He had to protect the Fellowship by bluster - actually fighting the creature takes time that they do not have.

Maybe Gandalf's statement was a grand poetic translation of:

"If you chase us, the sun outside will fry you."

Or maybe not. Maybe it was metaphorical: since they were both Maiarin in origin - flame - that only differed in masters - Udûn and Anor.

Once again, grand poetical way of saying:

"You cannot harm them as long as I am here."

Whatever the meaning was, Gandalf's bluster failed:

The Balrog made no answer. The fire in it seemed to die, but the darkness grew.

(LotR II 5)

Which is like saying:

"Where's your sun now?"

without words. But its fires seemed to die, probably realising that it cannot fight Gandalf's fire with his fire.