The Torah (Hebrew: תּוֹרָה, meaning "Instruction", "Teaching", or "Law") is an ancient Hebrew text. It is a compilation of five semi-related books (using their English titles): Genesis, Exodus, Leviticus, Numbers, and Deuteronomy. The Torah is the first main section of the Jewish bible, the Tanakh, and the religion's most important scripture. Many Jews place studying the Torah to be the most important thing a male Jew can do with their life (women have traditionally been barred from reading it). Jewish tradition presents the Torah in the form of a scroll, although it's becoming more popular to present it in the form of a book.
Despite growing up Christian and attending church hundreds of times, I was never taught that the Jewish Torah is essentially identical to the Christian pentateuch (first five books of the bible). The entire time I was a Christian I just assumed the Torah of some completely unique Jewish bible. It wasn't until I became an atheist and started learning about other religions that I discovered that three quarters of the Christian bible is really just Jewish scripture. My first readings from the five books was through a clouded Christian lens, but, once I learned that the books were written by Jews, for Jews, I had a very different understanding of them when I read them as an adult. I find the Torah to be a valuable, albeit myopic, example of human history and culture, however, I find the content to be truly revolting, and I'm disgusted at how Jews fetishize the work.
Authorship and Dating
According to the documentary hypothesis, the most widely accepted historical origin of the Torah, each book of the Torah is an amalgam of various sources, each with a different set of authors, that slowly came together over a period of several centuries in which the contents of the books were being frequently changed. Some of the sources date back as far as 900 BCE, but the bulk Torah's content was written around 600-500 BCE. As the compilation accreted, redactors made significant changes to the sources until around 400 BCE when the form that we receive today was essentially completed. Only minor changes occurred after that point. The oldest extant portions of the Torah that have survived are from the Dead Sea Scrolls which date back to around 250 BCE.
The traditional origin of the Torah is that the character Moses, while alone on a mountain, was given the majority of the contents of the Torah by Yahweh. Moses later wrote down what Yahweh told him and included the details of the Hebrew tribe up to his death. Those historians who try to mesh the fictional account of the Torah with actual historical data place it at around 1400 BCE. This origin was accepted without question by those who were raised in cultures dominated by the Abrahamic faiths until the 1800s, when historians started seeking evidence for the claim. Not only did they not find any evidence to confirm the story, they found lots of evidence that contradicts it, which is why the documentary hypothesis was created.
There are five books of the Torah, each consists of different themes and multiple writing styles. Genesis is mostly fanciful stories, most of which are borrowed from earlier cultures. It also contains lineages of men and their bizarre exploits. Exodus begins with more exploits of men, but includes long lists of prohibited behaviors. Leviticus is a work for priests describing how to worship Yahweh, make animals sacrifices to Yahweh, and atone for sins. Numbers describes the Hebrews slowly dying off because Yahweh forced them to wander in the desert. Deuteronomy is essentially a retelling of Exodus, Leviticus, and Numbers, but with notable differences.