What power is Elrond referring to?

[Ainaserkewen]

Yes, but "the Halfing forth shall stand" came in a more or less recent dream away in Gondor. Also, the spies from Mordor would have come after Bilbo attained the ring and there was hard core evidence that something was to happen. Gandalf said the watch was doubled so there was a watch previous to that around the Shire. Is there some kind of magic that happened to alert Gandalf prior to the events of "The Hobbit"?

And while it was brought up, the dream that Faramir and Boromir share...where did that come from? Does the future just show itself to people every now and again like any other fantasy book, or is there evidence that that was deliberate?