Everyone suffers in some way in Disgrace, and suffering takes place in a number of forms. Multiple examples of physical suffering pop up through the book: the goat with the infected scrotum at the animal clinic bleats in pain (we know, ew); David withstands being knocked out and set on fire; the dogs in the kennel are viciously executed, except for one that just lies there bleeding to death and waiting to die. These are all disturbing examples of physical suffering, but it's also important to think about the role that emotional and mental suffering plays in the novel; it seems that nobody escapes without some serious psychological wounds. While we don't witness Lucy's rape firsthand, we see how it changes her into a mere shadow of her former self who patters around the house and refuses to see people. David's own worries about Lucy constitute a major source of suffering for him. These, of course, are just a couple of examples of how suffering afflicts the mind as much as it does the body.
David's suffering allows him to become more empathetic towards others.
David's suffering makes him focus even more on his own problems.