Barre was a sadistic monster.
Barrie's treatment of Grandier was very 'over the top'. I heard that Ken Russell even edited a scene out where Barre beats up Grandier to a pulp with his fists. I guess they figured the torture of smashing his legs, picking him up and tossing him from out of a hammock to have his body rolling down a ramp wasn't enough. So they had Barre exercise all the torture until the finale when he sets Grandier on fire.
I'm curious to know if Ken Russell wanted to implicate some sexual frustration on Barre as well. think about it. He was effeminate and appeared jealous of Grandier's sexual prowess. Maybe he was even attracted to Grandier while being envious. His treatment of Grandier,after the trial, is one of dominance, jealous rage and sadistic zealousness.