Why has no one even suggested that Elbereth, or Manwe, or one of the other
Valar may be responsible? Don't the Elves and Gondorians still turn to
the Valar for aid? Sure, it might be Eru himself. Gandalf or
Galadriel I very much doubt, since there is no hint of it elsewhere, but I
suppose it is possible. But why does no one even suggest that the Valar
could be involved? Have I missed a line somewhere saying the Valar have
turned their collective backs on Middle-earth? Are people for some reason
uncomfortable with the idea that the Valar are, from a distance, still active
in Middle-earth?
I would say Manwe and Elbereth/Varda together are responsible for Frodo and
Sam's renewed strength, and for calling them to their feet/feat. It is
grace, yes, but grace dispensed by the Lord of the Winds and Eagles, and the
Lady of the
Stars.
“I dislike Allegory - the conscious and intentional allegory - yet any attempt to explain the purport of myth or fairytale must use allegorical language. (And, of course, the more 'life' a story has the more readily will it be susceptible of allegorical interpretations: while the better a deliberate allegory is made the more nearly will it be acceptable just as a story.)” (From Tolkien Letter # 131.)