It is the truth as Gadriel knows it. There's one way to stop Chaos and that involves violence. Prayer is to prevent corruption from taking root. Once it has, only a bolter can help.

Or a flamer. That would likely work too.

"It is fortunate that I failed in my endeavor." He was like 2 seconds away from removing the top of Titus's head. "I still await proper penance for my misdeed." That...will not be fun. Not that anything is in his world.