Yeah hmmm.... I'll say this much because the manhua has already shown Ash discussing it so therefore it's not a spoiler. Roland and crew already have the power to defeat the church as their greatest weapon is technically the judgement warriors. These judgement warriors, as you've seen in the latest chapters, can only be created in limited number because they require a witch to be drained of blood and even then, the person being turned into one of those mindless warriors may not survive the process. It's just a matter of time for Roland to manufacture better versions/more of his weapons while the church is using a method that requires a lot of resources and has an unsure success rate. Roland is using his image as a fool to have the rest of the world believe there are bigger fish to fry because what he needs most is time.
As for what that tower has to do with anything, it is a big secret and you are also correct that it's related to the church but it doesn't give them the sudden power to defeat them.

I have this feeling there's a secret in that tower with the demon's =_= some secret that would turn the tables on the church, but we won't know until they visit the place again to "save" whomever is in trouble inside.