what is the significance of ruth's attendance at david lee preston's wedding ?

"The book closes with a meditation on James's friendship with David Lee Preston, a Jewish reporter and the only son of a Jewish woman who survived the Holocaust by hiding in the sewers. David asked James to bring his mother to his wedding, so Ruth attended the ceremony as a guest. She said to her son: "You know that could've been me.""

sorry but i didn't got the answer