Why does Professor Cohen never use one of her vases?

Professor Cohen has one vase that she never puts anything in it. When her third husband invited her to his parents', she overheard his mother criticizing her and saying that she was cold, too intellectual, and barren. Later he came by her office with that vase and nothing inside. When he told her that it reminded him of her, she asked, "Cold, hard, and empty?" (194). He told her that the vase was a work of beauty. It was full of life, yet able to hold so much. It was perfect all by itself just as she was.