All of this has happened before. All of this will happen again...
Here is my theory: All humans are descended from cylons
Everything that has happened is happening according to a predetermined 'script' that repeats its self every couple of thousand years. The cylon God is the writer of this script.
I don't think it has been mentioned how many Gods the humans have but I'm guessing that it would be twelve. Each one of these Gods would have been based on a cylon model who goes on to seed each of the 12 colonies. The colonies develop and evolve and go on to invent the next generation of cylons which in turn go on to rebel/retreat/return and wipe out the colonies allowing a few thousand to escape.
The reason that the humans and the cylons arrived at the Temple of Jupiter at the critical time is because there are obviously hidden cylon models still making key decisions for humans (probably Roslin because the prophecies speak of her and the Xena type would certainly feel the need to apologise to her after nearly executing her on New Caprica).
The fleet that is escaping for Earth will become the new 13th colony and each type of cylon will go on to seed colonies 1 to 12. (This is why they have the obsession with human/cylon half-breeds.) Humans will evolve, invent new cylons, etc...
The reason that the final 5 cannot be revealed at the present is because they still have their unwitting tasks to perform. i.e. manipulating both the humans and cylons into doing what they need to do in order for everything to go according to the 'script'.
All of this has happened before. All of this will happen again...