Why did the Bishop sell the silver salt-cellars?

Why did the Bishop sell the silver salt-cellars?
or
How did the Bishop extend help to Mere Gringoire?

The Bishop was a kind-hearted man who always rendered help to the needy. He sold his silver salt-cellars in order to help Marie’s mother, who was unable to pay her house rent. He used the money that came from selling the salt-cellars to pay off the poor woman’s house rent.