The book invokes the pagan notion of a pantheon of gods, rather than the Judeo-Christian God. He describes a ritual where he propitiates the Muses (the gods of creativity) before sitting down to write. You might find it easier to swallow, because when people invoke the J-C God they often mean it completely literally, while the Muses are clearly allegorical.
But to get through the book, you have to suspend your rational empiricism quite a few times. Perhaps no more than to read The Odyssey or Macbeth, where internal human struggles are illustrated with supernatural imagery.
Many of the greatest human achievements in both art and science have had explicitly religious motivations. I'm an atheist myself but it seems like it might be worth exploring / understanding that if one wants to achieve something great. I've no idea if this book is helpful for that - I've never read it though I have seen it recommended several times - but it seems like an interesting topic to explore regardless of one's personal religious beliefs.
Despite my own lack of belief, to my taste religiously inspired art and architecture of the past seems to reach a level of greatness that seems missing from much of the modern God-free stuff.
I think we are going off-topic, but: 1) a lot of old art was commissioned with religious themes, regardless of artists' feelings, because that was the socially-acceptable thing to do; artists simply illustrated stories, giving it a personal spin. They are more akin to, say, illustrations for a modern movie production, than to a Warhol or a Duchamp. You might be responding to that. 2) if your parameters of greatness include "life-likeness", anything since the invention of photography will be disappointing, because artists stopped trying (they obviously couldn't compete); and 3) democracy freed artists from having to convey The Message, be it God, Nation, Progress or whatnot. Left free to choose topics, artists moved in other directions. Contemporary art is very cerebral and polemic, all the fun and sentiment is in pop.
I read this book this week. Its not well written, the „wisdom“ in it could be broken down to one page, and the religious explanation leaves a bad taste. Still there are some parts in it which are true imho and are often forgotten. For example that its necessary to be not cynical about your work, and treat it like something valuable which is not owned by you. To leave your ego out of the work and do the work for the work.
But to get through the book, you have to suspend your rational empiricism quite a few times. Perhaps no more than to read The Odyssey or Macbeth, where internal human struggles are illustrated with supernatural imagery.