Hola, lathspell, long time no see
My complinets to all other contirbutors of the thread
Two minor points to add (being in general agreement with lathspell, as it is):
1 Jewel on the end of Gandalf's staff is movie convention, I do not recall it mentioned in the books (anywhere)
2 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. Simply put, he tried to scare Balrog away. Sophisticated kind of Tom Sawyer "my brother can beat you up with his little finger" talk. Otherwise, as it was pointed up there, if he succeded in putting Balrog out, it would not matter what he told it before.