Means he's one of those holy men who go around tellin' everyone to give up the old ways and be like them.

[As a Wolfwalker, Mebh has little interest in that, especially since her ancestors' refusal to convert was what caused them to become Wolfwalkers in the first place.]

Her husband had more bulls, and she didn't want her husband havin' more stuff than her, so she tried to get a bull from somebody else. But he wouldn't give it to her, so she started a war against him.