By threatening to take your grace away, probably. Or undoing whatever it was he did to it, so that it'll start killing you from the inside. Or maybe he has some other plan, I don't know.
If we're all going to get through this in one piece, we've got to stick together, okay? So tell me what he asks you to do, and what he's threatening you with. And definitely let me know if your grace starts to hurt you.
[...] I'm leaving medical, whether they like it or not.