How is the cross in Mattie's living room thematically significant?

Is this the passage you are inquiring about?

"Every surface was covered: tables, chairs, walls. Over the fireplace there was a big cross made up of hundreds of small, brightly glazed pieces of tile, each one shaped like something: a boy, a dog, a house, a palm tree, a bright blue fish. Together they all added up to a cross. I had never seen anything like it."

Is so, all of these things together represent home and beliefs.