It's a challenging and perplexing read. My best attempt to summarize it briefly is "Foucault's Pendulum with black people".
"Nobody trusts anybody now, and we're all very tired"
It starts with an epigram from The Thing. And this provides some key to understanding some of the deeper meaning.
On the surface, an ex(?)junkie leaves his job cleaning bus station toilets to find himself at The Library, where he gets inculcated in a cult of sorts, sorting through newspaper articles to find traces of the messages that are being transmitted from The Voice.
Ultimately he gets promoted from researcher to agent, and is sent to stop a former agent gone bad. He's sent off with a female colleague who has her own story. We learn both of their backstories through flashbacks as they get closer to their target. He had a terrible experience growing up in a more traditional religious cult. All of the narratives past and present have a thread of who to trust, what is true, even while more and more 'paranormal' things begin to happen. Obviously this ties in to the epigram.
I think the deeper meaning, though this may be me reading my own skepticism into the book, is to doubt the things one is told, as opposed to the things one has experienced.
Not sure the book entirely works on either level, but it does get the gears in my head moving about in new and unaccustomed patterns, and that's always refreshing.
I slept with faith and found a corpse in my arms on awakening;
I drank and danced all night with doubt and found her a virgin in the morning.