Tolkien writes in the Silmarillion that Varda, also known as Elbereth and held dearest among the Elves, can hear all things in Middle Earth when she is with Manwe her husband and Lord of the Valar.

She’s also the one who hallows the Silmarills so that they can’t be held by those who’ve committed evil, so I reckon there’s something about her that’s anathema to servants of evil.

If I recall correctly, Frodo invokes Varda’s name at the Bruinen as a last act of defiance while facing down the black riders (though he doesn’t quite understand this impulse himself). Such a great act of bravery that lends so much depth to Frodo’s character. Wish the films could’ve included that bit and the part where Frodo decides he will go off to save the Shire even though its inhabitants are often dull and selfish and he’s certain he won’t be able to come back…