Evil Spirits are the product of the incomplete rules of the Flame world during the Age of Flame.
As the era changed, so did the rules of the world, and these beings also gradually faded out of existence.
In this current Age of Metal, the only remaining supernatural power was that of Pugilists. For the sake of his own continuation and status, while Eldridge calls himself a 'God', he had actually become a Pugilist in nature.
The ability he obtained from the Last God that allowed him to reinforce himself through faith has been altered by Eldridge into a Pugilist school of techniques, called the School of God.
Manifest a fake Seed of Pugilist through his followers' faith, then bestow them to the pastors and knights under him, thus creating a positive feedback loop.
The Age of Metal is also the age of Pugilists, and this was only the beginning of the era.