From the wiki, Iovara quote: "with their mastery they crafted their own gods to fill the void, and sent missionaries to the corners of the world to spread their faith".
From the wiki too, without quoted sources: "utilizing a massive adra-powered machine at Sun in Shadow to harness the souls of thousands of Engwithans assembled in the chamber - men and women, children and the elderly, all they could find - spawning the known pantheon. Each of them was crafted from an ideal, to give the kith not one, but many meanings to choose from in life. The surviving Engwithans then sent missionaries to the corners of the world to spread their faith."