Let’s review for a moment the big picture so far.
In Galactica, Kobol is the ancestral homeworld of humanity. 2000 years prior to the series, 12 tribes left Kobol and founded the 12 Colonies. 2000 years prior to that (ie, 4000 years previous), a 13th tribe left Kobol to find a mythical planet named Earth. Each of the original 12 tribes corresponds to a sign of the Zodiac. 400 years after the 13th tribe left (1600 years prior to the Exodus, 3600 years prior to the events in the series), the oracle of Pythia recorded her famous prophecy about the exile and rebirth of humanity, some of which is written in past tense.
Kobol was ruled by the Lords of Kobol, which correspond to the Greek and Roman gods of mythology. These Lords were apart from humanity, but not immortal or super-natural, and could also die (for example, Athena committed suicide after the Exodus of the 12 tribes).
It is also known that there was one Lord of Kobol, known as the “Jealous God” and also as the one whose “Name must not be spoken“, who desired to be elevated above the other gods. This god’s ambition is what precipitated civil war on Kobol and led to the Exodus of the 12 tribes.
As Galactica retraces the steps of humanity, they discover Kobol, abandoned 2000 years previous. Moving onwards, guided by the Book of Pythia, they discover progressively older artifacts – a beacon in the Lion’s Head nebula dated 3000 years ago, and then the Temple of Five dated 4000 years ago.
What follows is my theory about the above, and the origins of Cylons and humanity. Since it is ridiculously spoiler-esque, and discussion of it will also be spoiler-laden by necessity, I am putting it below the fold. The key, however, is simply this: The Cycle of Time.
“If you believe in the gods, then you believe in the cycle of time that we are all playing our parts in a story that is told again, and again, and again throughout eternity” (Kobol’s Last Gleaming, Part I).
Or, as it is said in the Pythian prophecy, “All this has happened before, and all this will happen again.” In addition, the very first line of the Sacred Scrolls states, “Life here began out there“. These broad concepts are the key to answering downstream questions such as Who are the Final Five and the identity of the Final Cylon.