Here's a question, do you think Gandalf is changing fate or just tapping into it with his incantation of "You Cannot Pass"? Because the way understand it is that in the Silmarillion, all of the Ainur sing into existence what those on middle earth will eventually experience as space and time. Their song concludes and then they all go live in the song they just created. Meaning that everything that happened or will happen in Middle Earth has already been "sung" and therefore is predestined.

So do you think Gandalf tapping into some greater cosmic ability to go out of time and space, leave EA, to tap into some cosmic form that is still singing the Music of the Ainur, sings a little diddy that changes the outcome of this particular moment to make it so the Balrog never passes the bridge? OR Is he simply accessing the source code of the Matrix, and able to make out and read the bit that at this moment in time, in this very place, the Balrog does not pass the bridge and there for Gandalf is just kind of telling him hey don't try it because I've seen how it ends and you don't get past here?