Quietly, to Strange's initial question: "Attempting a Harrowing and failing it means instant execution." It's a thing he didn't think to explain, a fundamental property of the way Circles used to work. "The idea, on paper, is that Harrowing proves a mage can withstand demonic temptation. That they have enough control that their power doesn't make them a danger to themselves or anyone else."

It's best it's come up, probably; in Julius's mind, it's impossible to understand Circle mages without understanding what Harrowing had been for them. Why some would choose Tranquility rather than risking it.