That is the part that was complex.

At the time, I was on a world much like this; the original inhabitants were long dead, leaving only their deities behind. In order to show us that world's past, one god within their pantheon worked with his long-dead sister to cause what remained of their peoples' spirits to merge with ours. This served a double purpose of both transferring their knowledge, and enabling those ruined souls to be able to find some measure of peace.