The motif of chronic pain
When J.T. Malone finds he has a debilitating, lethal disease, he was already suffering a season of confusion from his failure in med school. Judge Clane has a host of health issues. For one, his obese body causes pain in his old bones. Then there's his diabetes. Plus, he lives in the aftermath of a stroke, which is no small thing. All this constant pain represents the constant pain of life, but more importantly, it symbolizes the dying era of unbridled racism in America, and the chronic pain of the continual work of racial reconciliation.
Judge Clane as the symbol for hatred
There's no doubt about it. Judge Clane is an archetype. He's the satanic archetype, the man whose pride causes him to think he's God, and that he's above judgment. However, if his declining health is any indication, he's not as indestructible as he thinks, and one sort of leaves the book hoping there is a God out there who can judge men like Judge Clane who use their hateful power to destroy innocent people like Sherman Pew.
Segregation and integration
In the novel, integration represents forward progress, where as the Confederate-loving, past-oriented Judge is still locked in a former way that is simply outmoded. As a motif, the question exists in other ways too, such as Sherman belonging in a white community, or the USSC's decision to forbid segregation in public schools.
Martha as the reward of good
Because J.T. Malone chose to face death like a man, choosing to prioritize his family and his simple, detached demeanor, he is award the pleasure of company when he dies, and not only that, he earns honor from others, whereas the Judge is only awarded praise from other hateful racists. Martha is therefore a symbol for a higher sense of moral good, and the award of a life well-lived.
The motif of death
Whether death by cancer, death by terrorist attack, or death by stroke—no one escapes this earth without dying. Death comes to represent the ultimate standard for moral goodness in the novel. The characters who act like they are god are racists and violent, hateful people, but Malone faces death humbly, making things right for his departure.