Put more plainly, Barbelith is represented in The Invisibles by a big red
circle that turns
green when it thinks you're ready to enter the
Invisible College. (Said college being a liminal space between this universe and its evil twin, not something you enroll in.) Sort of a
traffic signal of the gods. As the series rolls on, Invisibles author
Morrison makes it more and more clear, in part through typography and caption-styling, that Barbelith itself has many more
speaking parts in the series than was first evident. Characters in the book tend to see it when they have some sort of radical
satori, although certain adepts like
King Mob seem to be able to travel to its space at will.
Barbelith is also a web site (barbelith.com, natch) wherein the entire run of The Invisibles has been annotated and (sort of) explained in the subsection entitled The Bomb. The front matter of Barbelith includes editorials and links related to the worldview that Grant Morrison espouses in the book, and occasional features on other comic artists whose work is vaguely related. The Bomb subsection features all sorts of enlightened riffing and rambling on every nuance of virtually every page of the comic series. It can greatly improve one's comprehension and appreciation of the work, except when it leaves you more confused than when you started.