@antimatter, I don’t think it’s correct to say “the Bible was rewritten several times.” Or at least that’s a huge oversimplification.
The Bible is a huge collection of documents. Broadly, it can be divided into the Old Testament and the New Testament.
The Old Testament. The earliest of the Bible’s documents—parts of Genesis and Exodus, Job, and the Psalms—come from oral poems, myths, and laws told by a tribe of bronze-age nomads called the Hebrews.
These oral poems and stories, in turn, were often based on even earlier Mesopotamian myths and laws. For example, the flood story in the Bible is modeled on earlier Babylonian and Sumerian flood stories. The god of the Hebrews, Yahweh, has many of the same traits as earlier Mesopotamian gods such as Marduk, Enlil and Sin. The cult of Sin, the moon god, practiced “Shabatu” days similar to the Hebrews’ Sabbath. The legal code in Exodus is very similar to the earlier Code of Hammurabi, supposedly given to a Babylonian king by the sun god Shamash.
So you’ve got all that stuff which evolved from Mesopotamian mythology and existed for hundreds of years mostly as spoken texts.
Then you have the “Deuteronomistic texts,” which includes the book of Deuteronomy and the historical books that follow it: Joshua, Judges, Kings and Samuel. Those were composed later, probably around the time of the early Jewish kingdoms.
Then, around the time of the Jews’ Babylonian captivity, the “prophets” section of the Bible was composed—Ezekial, Daniel, etc.
It’s not exactly clear when all this stuff was first written down. Clearly most of it was floating around as oral tradition long before it was written. Some scholars put the date of Genesis first being written down as late as 400 B.C.! We don’t know for sure. What is clear, however, is that the written Old Testament we have now is the result of multiple “editors.” If you look at Genesis, for example, you’ll notice that parts of the text have a distinctly different style than others. Genesis 1 consistently refers to God as “Elohim” and reflects a certain worldview; Genesis 2–3 consistently calls God “Yahweh” and reflects a slightly different worldview. (fyi Genesis 1 is called the “Priestly” source, 2–3 is called the “Yahwist” source.)
On top of that, there are a few sources that are included in some “versions” of the Old Testament but not others. These are called “apocrypha” and they only appear in certain Bibles because people of rival religious traditions think they don’t belong.
The New Testament contains writings pertaining to a Judean cult that resembled a cross between Judaism and Roman mystery religions, centered around the historical cult leader named Jesus. It can be divided broadly into two parts: the gospels and the letters. Oh! And almost forgot, the funnest book of them all: Revelation, modeled after earlier prophet texts in the OT.
The earliest documents in the New Testament are actually Paul’s letters. Paul co-opted parts of Jesus’ cult (he never met the guy) and his earliest letters date to around 50 A.D. None of his letters deal much with Jesus’ life or teachings; they are mostly concerned with the idea, found in many mystery religions, that Jesus died and was resurrected as a salvific act. A lot of it is theology, trying to reconcile this idea with Judaism.
Some letters, such as Hebrews, are sometimes attributed to Paul but they are actually much later and not written by him. It was a common practice in ancient times to write documents and then claim famous people (such as Adam or Enoch) wrote them—a practice called “pseudepigrapha.”
The gospels are basically legendary documents that chronicle the life and teachings of Jesus. The earliest, Mark, probably dates to around 80 A.D. Matthew and Luke both copy a lot of Mark’s text (and occasionally correct and improve his sloppy Greek prose) so scholars conclude they came later. John is completely different from Mark, Matthew and Luke and scholars think it comes even later.
The book of Acts is actually the second part of Luke’s gospel and was clearly written by the same guy.
About the gospel authors: they are not the historical Mark, Matthew, Luke, and John. Those names are found nowhere on the earliest documents. We have no idea who wrote them, or if any are the work of a single author at all. Rather, the idea that they were written by these people is a later church tradition.
On the Bible’s truth-value. The first part of the Bible is clearly Mesopotamian mythology. Yahweh is a standard Mesopotamian deity. The earth is described as flat; the sky is described as a solid dome that holds up an ocean. The sun, moon, planets and stars revolve around the earth. There are talking snakes and donkeys. The Babylonians, like the Hebrews, believed their ancestors and ancient kings lived for hundreds or even thousands of years, and believed in a cosmic flood that reset creation.
The Exodus story may reflect an actual movement of people from Egypt to Canaan. Just before the earliest mention of “Israel” in the archaeological record, there was a short-lived monotheistic cult in Egypt based around Aten, the sun god. It’s entirely possible that believers from this cult (which was later outlawed) emigrated from Egypt to Mesopotamia and mixed their religious ideas with the mythology found there; I personally think this is likely.
But the Exodus story is a legend at best, if not an outright myth; there is nothing in the historical or archaeological records to support its most basic claims. It’s not even clear that there were Hebrews at the time.
The laws found in the Old Testament are barbaric by any standards, even by ancient times. They promote slavery, rape, and genocide. In fact, the Bible is the only religious text to command genocide.
The New Testament’s gospels may seem like “historical” documents but they contradict each other and are unsigned, undated, and their fantastic claims are uncorroborated by any evidence from the period. It is also worth keeping in mind that “history” as we think of it did not exist back then. Even official historians who signed their documents would claim things like “Emperor Vespasian healed a cripple and a blind man” (from Seutonius) or “before the Romans attacked a cow gave birth to a donkey and there appeared a floating army in the sky with chariots” (Josephus).
Aaand I can’t believe I actually wrote all of that.