For the past couple weeks I've been reading Christianity: the First Three Thousand Years, by Diarmaid MacCulloch. It's a massive tome of a book, so I'm only a couple hundred pages in, and thus a couple hundred years into post-Jesus history. Two related topics have really struck me: the nature of scripture and the diversity of early Christian belief. I never really thought about these things back in the day when I was a believer, and so I assume your typical, theologically untutored believer also hasn't thought much about them.
Admittedly, I was a lazy Christian growing up,* but I expect my own experiences with scripture are fairly common, even among life-long believers. When I was a wee believer I more or less didn't read the Bible at all. I absorbed everything I knew about Christianity from the culture around me: my parents, Sunday school, television, other books, etc. These included vague ideas like the existence of Heaven and Hell, and the necessity of "accepting Jesus Christ as your personal savior" to enter the former and avoid the latter. God was all-knowing and all-powerful. And benevolent. Things like this. I just assumed all this was in the Bible, and the Bible was written by people inspired by God.
I had a more sustained exposure to scripture during my high school years. I must have read a lot of passages, especially from the New Testament, during the sermons and the young adult Sunday school sessions, but to be honest I don't remember much of which selections were covered. This was all just the Bible, mostly amorphous except for the distinction between the Old and New Testaments. I guess I knew that the OT was a history of the Jewish people. And the NT covered Jesus's time. And Revelation was a vision of the future. Even when I heard the full names of the NT books, like Paul's Letter to So-and-So, I didn't really stop to grok that this was a letter, like the kind one person writes to another. These books--letters or whatever--were the inspired word of God. I would ignore the broader context and mull over whatever point the pastor was trying to make.
Reading Robert Wright's book and now McCulloch's, you can't help but really grapple with what scripture is. Those NT works really are letters. They're letters from early Christian churches to one another. Why are they writing each other? Because they are trying to figure out what the hell it means to be Christian. No one knew at the time. They were letters written a few decades after Jesus' death. And the gospels, those recounts of the life and times of Jesus, were written after many of these letters (the whole Bible is completely out of order, turns out). As there were more gospels and letters written than are included in any one version of the Bible, different churches argued and ultimately disagreed on which ones should be deemed scripture.
This whole process took a couple centuries, and clearly there was no hard and fast reason for it to stop, but now there is a lock-in effect, whereby what is scripture is scripture, and everything else is literature written about scripture. It's interesting that there is no inherent difference between the scribblings of later theologians (like Augustine or Rowan Williams), the communications of modern church leaders like the Roman Catholic Pope (or the Pope of Alexandria), and what modern believers think of as scripture. Summary point: scripture is a lot more organic than the naive idea I had growing up, where I took it more or less as is.
The other big thing I got from reading about the early churches is just how incredibly diverse they were. These churches weren't just arguing things like whether Jesus had two natures or one nature (whatever that means). They were arguing about whether they were still Jews or not. Gnostics believe(d) that Jesus was sent by an entirely different god to save us from the flawed creation of the wicked Jewish god. Ethiopian Christians revere(d) Pontius Pilate, of all people, for their own peculiar reasons. One of my favorite theologians I've read about, Origen, thought that all mankind would be saved, and not just Christians (remember, this guy's writings could have been scripture). He viewed Christ as subordinate to God. And he also, like me, never could figure out the point of the Holy Spirit, ultimately leaving that as an exercise for the reader. Reading McCulloch, you appreciate how wildly different modern Christianities would be if history had taken a slightly different course at various times.
As I assume 95% of my readers are non-believers, I'm not really trying to convince anyone of anything here. I'm just getting a kick out of the history, and recommend the book as a good way to learn a little western history from the angle of Christianity. I blogged about Robert Wright's book here.
*Lazy only in some ways. I internalized hard the notion that people I cared about were destined to suffer for eternity, and that it was mighty unfair for people born in other parts of the world to suffer the same fate. And I had a fairly sophisticated argument for how free will and an omnipotent deity were mutually incompatible.