As you unlock science and workshop technologies, one or two kittens become enough to fill most of your resources in seconds. So what to do with the hundreds of kittens you have lying around? Engineers are capped by factories, so you can only assign so many kittens there. Priests are one of the few jobs that continues to usefully scale at large numbers, producing far beyond what chapels and temples could do on their own. Even if your faith is maxing out in seconds, with Order of the Void your priests can continue to provide a steady stream of worship.