"Do you have some reading suggestions about religion?"
Here's is my typically wordy response:
The One Text?
I have real trouble finding the "one text" that is a tell-us-everything example to rule them all, and in the darkness bind them, so to speak. I find it an interesting introspection trying to single out a pivotal moment. Perhaps for me it was more the accumulation of equivalently justified yet contradictory ideas that lead to my suspension of belief about any of them.
What really cracked my comfort zone forever was chapter 6 of Irving M. Copi's Symbolic Logic (I think it was 3rd edition) in which he, seemingly out of the blue, talks about logical systems. But reaching that point relied on surveying many "systems" of thought and finding them all to be based on principles that were themselves subject to effectively unanswerable questions and in principle unprovable assumptions. So reading that chapter was the little, but decisive straw that broke the camel's back, so to speak.
This Math Crap
Now couple this with the answer to the question every despairing high school kid asks, 'Why do we have to learn this math crap anyway?" Well, one answer is that if you understand this math crap, you effectively understand the basics of pretty much everything ever done in any other area of human understanding - and that includes religious theology. Math has such incredible utility, that, as an academic enterprise, we have been attempting to turn everything into mathematics, even language. Logic goes by another name, and that name is propositional calculus. A mathematics of language. Change the operators from "+,-, =" to "and, or, not" and take the propositions as numbers and you have logic.
Analytic vs Synthetic
And then another realization comes to the fore: these are all language structures with no necessary connection to reality. Some seem to "map onto" reality better than others - offering something called predictive power. Others, including almost all faiths, not so much so. The point of faith is, after all, to justify belief when no or little connection with reality exists.
I tend to think of a logical system as being like a spider web hovering over reality. Some touch reality at times and others are completely divorced from reality altogether. Those that touch reality allow for reality to determine the content of the logical system. Those that don't, well they are entirely fabricated works of fantasy. However intricate, elaborate, attractive or beautiful they may or may not be, if they do not touch reality, then they are nothing more than flights of whimsy.
And then there was analytic ethics, and I don't even recall the text I studied so long ago - I suspect that any good introductory text will be useful in introducing what are thought to be the cornerstones (prescriptivity, universalizability, etc.) of ethical systems as well as introducing several such systems, from prescriptivism to emotivism and possibly including deontic logic (a symbolic logic of ethics such that ideas like "permitted," "obligatory," and "not permitted" are taken as truth-values). Analytic (meta) ethics trains one to look at the systems of ethics independent of the ethical content itself - and that's just a whole other kettle of fish.
Oddly enough, it was "Dianetics," the pre-scientology scientology book that really showed me the fallacy of religion. The concept of the "engram" qua "moment of pain that inhibits the perfect calculating machine" was a concept that is neither refutable nor verifiable, in principle, and it leaped out at me from the pages as the flaw it was. It was a God-concept that became my standard for comparing other elements in religious theories, and when I went looking, I found them. I see them everywhere now. This is, actually, part of the reason I do not see it as necessary to read "holy books." I've already seen the one-trick pony perform and I am not inclined to read thousands of pages just to see the idiotic trick routinely performed again.
What science does is it refuses to allow that one-trick, by calling for evidence, and because of that, it cuts through religion like a hot knife through butter. The one-trick is "in principle irrefutable/unverifiable ideas." It could be engrams, it could be god's will. It could be self-interest, it could be causation in hard-determinism. Either you are permanently impressed by the one-trick or it never impresses you again.
One Path Among Many
There are as many different paths in development as there are people to walk them. Few people, I think, will claim that they spent 3+ years striving to excise normative language from one's discourse, like I did. Yes, I tried to eradicate shoulds, oughts, good, evil, better, worse from my "natural discourse."
I no longer see the world in terms of truth, but rather in terms of stipulated definitions, axiomatically presented, and tied together with tentative rules of inference. If that seems fragile, it might be because it is. At the deepest levels, everything is wide open.
When it comes down to it, I think what lead me away from religion is not so much any one book or event, but an accumulation of experience, whether it be academic or normal life. Breadth of experience promotes distance between oneself and any one perspective - to the point that the breadth of experience itself becomes the perspective.