Vergil didn't originally plan to get involved with cults. It might be a valuable source of power if they believed in him, but he wasn't going to gather fanatics around him for the sake of a few bits and pieces. Slashing demons and sucking the power out of them was a more reliable and tried-and-true method, and he wasn't about to change it.
Until he began to notice how, during battles with demons, people in black hoods flashed around more and more often, as if they were waiting for his defeat. They got more and more brazen, getting in the way and throwing themselves at him, confident that he would be a worthy gift to their gods. They died with a smile on their lips, knowing that their brothers would not rest until the blood of Sparda's heir was spilled before the altar. That's when Vergil decided to deal with them.
Finding out exactly where was their temple wasn't too hard. Vergil, in a black cape, crossed the threshold of the temple. Inside the temple, a whole crowd had gathered and were watching something in sepulchral silence. Vergil frowned and tried to squeeze closer to the center of events.
The altar was covered with a pool of blood, and on it lay the corpse of a young girl with her organs disemboweled. When all the blood had drained from her body, the leader shoved it to the floor and signaled to the deacons. The cultists literally dragged you to the altar. And Vergil, who had seen so many atrocities in his life, stared numbly at the scene before him. How dare they do this to almost children? They must have been under the age of majority... He woke up only when you had already laid down in the place of the previous victim. He jumped out of the crowd and was beside the 'priest' in a split second, chopping off his hands in one clear blow.
«If your gods allowed it, I'll kill them all!»
Vergil covered you with his back and stood in a fighting stance, glaring at cultists with an icy gaze from under his black hood. It's like he went berserk in the moment.