Sheʾol and its synonyms, בּוֹר “pit,” שַׁחַת “chasm,” and אֲבַדּוֹן “oblivion,” was the fate of all people upon death. The wicked were sent there early, while the righteous were rewarded with a long life. During the Second Temple period, the negative attitude about death and sheʾol develops into a concept of post-mortem punishment and eventually hell. 1 Enoch’s four chambers for the dead is the first step in that direction.
The story of divine beings procreating with human women (Genesis 6) is expanded upon in the book of Enoch to tell how these angels also bring sin to humanity, causing the ancient flood as well, and this sin is the source of disease in the present day.