Why was Boromir allowed to join the Fellowship?

[Tuor in Gondolin]

Originally posted by Nogrod
I think, adding Boromir (and what he does) adds also to the general idea, or worldview, that things happen by a sort of providence where every act has it's role.

Which touches on the interesting dichotomy in ME between predestination/Iluvatar's will versus free will. For example, Frodo was "meant to have the Ring." But he could have refused it. And Isildur could have chosen to destroy the Ring (rather messing up the LOtR, but...

Gandalf says somewhere, I think, that he would not consider himself to have failed if even a (flower?) remains to eventually redeem ME from Sauron. There is free will, which can lead to failures against Morgoth, Sauron, etc. But eventually Eru will repair the situation. Or to quote the Silmarillion:

Then Iluvatar spoke, and he said: "Mighty are the Ainur, and mightiest among them is Melkor; but that he may know, and all the Ainur, that I am Iluvatar, those things that ye have sung, I will show them forth, that ye may see what ye have done. And thou, Melkor, shall see that no theme may be played that hath not its uttermost source in me, nor can any alter the music in my despite. For he that attempteth this shall prove but my instrument in the devising of things more wonderful, which he himself hath not imagined."

Which really ticked off the bright boy in the class (Melkor).