Significance of blue beard?

This object has been retained by a cloister of nuns. It is the remnant of a powerful man who is of exceptional danger to women. He was a danger to other men by virtue of being a warrior, but his aggression against his wives, who were not warriors, tended to be dangerous or deadly.

It is only through the violence of other men that the man with the blue beard is defeated in his aggression against his sequence of wives. It is only due to the sufficiently early awareness of his newest and quite young wife and her sisters that his deadly nature was notices soon enough to have him defeated, instead of another woman ending up dead.

There is no explanation as to why his beard is kept by nuns, who live together in seclusion, mainly for reasons of mutual aid and protection.