a) People living in ancient times had very little understanding of science, as the Scientific Revolution hadn’t occurred yet (it began approximately fifteen-hundred years after the New Testament was written, and thousands of years after the Old Testament). They had a tendency to explain natural phenomena as events orchestrated by God(s). For instance, if someone had an epileptic seizure it would likely be attributed to demon possession. If a storm killed a bunch of people, it was God punishing them for their disobedience. The Scientific Revolution dispelled many of such myths.
b) Ancient people often used metaphorical language and exaggeration to illustrate a point. The Jewish people in particular had a long tradition of using symbolic language. The Book of Revelation is case in point. It’s pretty far fetched to believe that the imagery described in that letter is literal (I used to believe it is). That letter contains symbolic language, not literal descriptions.
c) The bible was written in Hebrew and Greek. When it is translated into other languages some of the meaning gets lost in translation.
d) Jesus didn’t speak either of those languages. He spoke Aramaic. Further causing meaning to get lost in translation.
e) Many of the stories mentioned in the bible were passed on through oral tradition for decades, or longer, before they were written down. Changes to the stories would have been made by those retelling them. Sometimes intentionally, sometimes inadvertently.
f) When stories were eventually written down, they were copied over and over again by hand for hundreds of years. Mistakes were made, omissions occurred, and changes were made. The story of the woman caught in adultery is a great example: it doesn’t appear in the earliest New Testament manuscripts. Someone living in a later generation added it. Another one is the ending of the Gospel of Mark: it was added later, because someone didn’t like the original ending (which didn’t include a resurrection sighting).
g) We have no surviving original documents. Only copies of copies, written hundreds of years after the originals.
h) Most biblical scholars agree that many of the books and letters in the bible weren’t written by the people we think wrote them. And some of them are complete forgeries (people pretending to be Paul or Peter, etc.).
i) There were many other Gospels written around the same time period of the four Gospels we’re familiar with. All of them, including the four we’re familiar with, were written anonymously. There were also several other books of Revelation, but only one was chosen to be included in the New Testament.
j) The four Gospels included in the New Testament contradict one another in some parts of the narrative, in terms of who did what and when. And they’re generally inconsistent with one another on details important to Christian doctrine. For example: there is no mention of a virgin birth in Mark.
k) Certain Christian patriarchs living hundreds of years after the death of Jesus and the Apostles were the ones who decided which books should be included in the New Testament (and not all New Testaments contain the same choices). The other gospels and epistles (of which there were many) were discarded as heresy, even though they had been regarded as scripture for hundreds of years by many early Christians.
l) The Book of Revelation was a metaphorical depiction of the conflict happening between the Jews, Romans, and Christians of that era. It was not a prediction about the end of the world thousands of years later. The Book of Revelation is so opaque that one can read things into it and easily apply it to one’s own generation. Which is what has happened many times over the past two thousand years since it was written. See Last Days Madness: Obsession of the Modern Church
Other sources:
Living With Confidence 