In a sense the Baron (who casually dumps things off of the bronze mirrored tray to provide a mirror for Grandier to take a last look at himself through a glass, darkly) does that act because he is not a devout believer. He needs the walls to Loudon to be brought down along with its beloved 'hero Priest' (who ironically is just a corrupt womaniser whilst he is being celebrated; and only becomes truly heroic once his trappings of privilege have been removed from him - contrasting with the King who does this as well at certain points, but only to expose himself rather shallowly and obviously either as a representative of a God or just as your simple humble 'Common Man'. It is the difference between Grandier's sincere (re?)discovery of faith and the King's vain playacting that is key in that contrast, along with the various audience's pandering or mocking reactions to the same), and if what it takes to do that is an accusation of possession and witchcraft, then so be it. Once Grandier is accused, the Baron does not particularly care whether or not Grandier's faith is fully destroyed, because the Baron himself does not believe in the afterlife, just the material world (which is why he is able to make the "Hell will hold no surprises for you" dig at Grandier). Even the other Cardinals and Priests - more concerned with upholding the regime than getting to the absolute truth of the matter - do not. The Exorcist, as the true zealot who has fully bought into the philosophy, does. Which is what makes his scenes with Sister Jeanne so upsetting, when she initially thinks they can just 'roleplay' together for their mutual benefit, but terrifyingly the Exorcist actually
means everything he does to her.
That is really what makes The Devils such an important and devastating film to this day. It is extremely political, but not about the superficial political aspects that characterise most 'Political' films in the sense of dealing with current events and particular political movements. In that respect it makes the film a bit closer to something like Silence, in the sense that it is about the deeper and more fundamental aspects about the age old conflicts between faith and society, and how each influence, and potentially can corrupt, the other.
That makes its fundamental messages continue to resonate to this day. Yes, there are parallels to be found that Booshman drew earlier to Trump politics (though as
MichaelB pointed out years before Trump the issue of religion intertwining so thoroughly with politics, mostly through patronage and funding, has long been an issue, whatever the figurehead). But the events this weekend in France, particularly the burning down of Limoges Cathedral, makes for some powerful parallels as well. Particularly the idea that the ruling classes of the society in some ways, and whilst of course officially decrying the actions as immoral and obscene, are party to encouraging the society to collapse to a certain extent. Because it is easier to remake society again the way they want it from the rubble of total devastation rather than just tinkering around the edges of a pre-existing society, which may actually have the temerity (and lack of humility) to actually refuse the changes mandated upon them. Particularly when city states are getting too self-confident with their fancy new walls and Priests getting to big for their britches, it all needs to be brought down, whatever suffering will be caused by doing so.
(I mean, if you want a slightly less highbrow reference, that is what makes The Devils and Asterix pair well together!)