As they can control a miraculous power called "Song Magic", they are said to be capable of "talking with the world". Every Reyvateil is connected to the Song Server they use as the source of their powers through an umbilical cord of sorts located in the deepest layer of their psyches.
The passage describes Reyvateil's unique ability to use "Song Magic" for communication and how they are connected to the Song Server via a psychic link in their minds.