[Zigûr]

I've always read this moment as nothing more complex than the "voice of duty" as it were - the part of Frodo, perhaps hidden to his conscious mind, which knew what he had to do even though he deeply did not wish to do it. Who would willingly take on such a terrible burden? Yet he knew deep down that he was the person who ought to do it.

I personally don't find it necessary to seek a supernatural explanation here. I feel like if I read such a thing in another work of literature I would take it for granted, and I take it for granted here as well. Magic rings or not, Professor Tolkien captures that moment in human experience when a person knows they must do something which is completely contrary to their own desires and wishes because it is the right thing to do.

That's how I see it.