Originally, the members of the Essencer Guild operated very secretly to prevent their existence from getting known. But the moment Essencer reclaimed all his power from them, they panicked.
After all, without the Devil, they would no longer be able to lead their happy lives. Those that prayed to the Devil were psychopaths in the first place, and the powers granted by Essencer allowed them to lead happy psychopathic lives.
If Essencer were to die, they would have to live like normal humans. But considering how their appearance wasn't human anymore, they wouldn't be able to blend in with the crowd like before.
Therefore, the members of the Essencer Guild thrashed through society, trying to hunt as many people as possible to supply Essencer with the faith and lifeforce they could collect. Of course, this only made it easier for the Aggressors and priests of faith to target them and put them to rest.