Who is Solace, Zuriel from Caleb's Crossing: A Novel and what is their importance?

Solace and Zuriel are two Mayfield children who die very young. Zuriel is Bethia's twin brother, killed in an accident, while Solace is her much younger sister, also killed by accident but whose birth was also the cause of Goody Mayfield's death. While Bethia is alive, she is determined to give Solace a better life than she ever had, but Solace dies too young for that ever to come to pass.