I'm not going to spoiler this, partly because it's speculation and partly because if you're in this thread you should probably have watched the whole thing.
The Lords of Kobol are the 'Angels' and the 13th Lord of Kobol is 'God'. We see a few of them throughout the show - Head Six and Not-Gaius, the Leoben Kara speaks to before she dies, the version of Elosha which Roslin speaks to during jumps. They're likely the leftovers of some previous cycle, from a group which managed to take resurrection technology to its logical conclusion - to create an afterlife or some kind of immortality.
Something happened on Kobol which made the 13th tribe (Cylons) leave for Earth, the other 12 tribes (humans) to leave and form the colonies, and the Lords of Kobol to abandon them all. In all likelihood it was a war between humans and Cylons, and something happened which made resurrection there impossible. It's mentioned that the Cylons which made their way to Earth were trying to reinvent resurrection technology, and it's mentioned that anyone who dies on Kobol is really, really dead. As in no afterlife for them.
The Angels follow the humans and Cylons around in the series, sometimes trying to nudge them in the right direction, sometimes outright influencing events to try and save what's worth saving of both races. Kara becomes one of them when she dies, likely a replacement of Athena, who God watched throw herself from a cliff and die in despair at the departure of the 13 tribes, or Aurora, whose idol she hands to Adama before she dies (a figurehead on the ship, leading the way much as Kara would later do for the fleet).
Or, you know, BIBLE IN MY SCIFI RAGE RAGE RAGE