I think the wife is upset because "going ascetic" means cutting off contact. The husband is sure he won't do it because the brother is talking about it instead of doing it, which he demonstrates.

It feels like there should be more to the lesson learned than, "people who have decided will act, people who haven't only talk," but I am not quite grasping it. Maybe the other part is, "and worrying about things you cannot change harms yourself," or something?