In Disgrace, David rediscovers his role as a father to Lucy both when she welcomes him into her home and when he finds that he has no choice but to take care of her after she's raped. Even though their personal relationship is strained, their familial relationship comes to the surface in a powerful way. Family is one of the most important means through which the characters of the novel support and protect each other; think also of the way that Petrus protects Pollux and how Mr. Isaacs storms after David in response to his treatment of Melanie.
In Disgrace, family love is complicated but unconditional.
Disgrace shows us the ways that familial love can be compromised and destroyed.