How does Joe Christmas fill the role of sacrificial lamb in the novel, Light in August?

From the time he is born, Christmas fills the role of the sacrificial lamb. His violently insane grandfather prevents anyone from going for a doctor as Christmas' mother dies in childbirth. Christmas' grandmother is powerless to prevent her daughter's death, or to stop her husband from abducting the newborn baby. The grandfather, Eupheus Hines, dumps the baby on the doorstep of an orphanage on Christmas day, then spends five years working incognito as the orphanage's janitor, while keeping an evil eye on Christmas. When the innocent five-year-old witnesses something he doesn't understand, the orphanage's female dietician becomes convinced the young boy is trying to blackmail her for catching her in a sexual tryst. Ignorant to the boy's innocence, she conspires with the janitor to label Christmas a negro and have him sent to a negro orphanage. Whether or not the boy has any negro blood in him is never proved or disproved. Nevertheless, it becomes the reason for all the subsequent persecution and scorn which is heaped on Joe Christmas.