In her work "Uncle Tom's Cabin": Evil, Affliction and Redemptive Love, critic Josephine Donovan says that the main theme of Uncle Tom's Cabin is "the problem of evil [shown on] several levels: theological, moral, economic, political, and practical." Almost certainly, Harriet Beecher Stowe, in writing the novel, set out to show not "the problem of evil" but the problem of a specific evil: the enslavement and use of human beings as the property of other human beings. In order to accomplish this goal in an effectively dramatic fashion, she could not merely present slavery as a monstrous wrong, chewing people up and spitting out what remained of them, physically and spiritually; she had to show it in conflict with a force that she knew to be more than equally powerful: the love of Christ. The theme of the novel then (not a simple theme, either, because of the levels Donovan enumerates) is this conflict.
Slavery is a powerful wrong. It is said to be wrong — in all cases, notwithstanding fair individual treatment of slaves — throughout the novel, first by George Harris, later and at length by Augustine St. Clare, and always by the narrator, directly as well as indirectly through the use of irony. It is shown to be wrong from the beginning of the book, despite the relatively benign setting of Shelby's Kentucky farm; again, individual slaves in individual cases may be well treated and even happy in their situations (as Eliza apparently has been), but the institution not only allows but is entirely based on the objectification of all slaves as commodities. Such objectification is evil, in the kind of actions it permits and supports and in the spiritual damage it does to individuals.
Because Shelby, portrayed as a decent if somewhat shallow and thoughtless man, is in debt, he is forced — according to law, because he owns property — to sell some of that property. The fact that he is also selling, as Chloe says, "heart's blood, heart's love," is, by that law, irrelevant. Shelby and Haley are introduced as a pair of opposites, one a "gentleman," the other a crass materialist of no sensitivity or cultivation. In fact, their participation in slavery makes them (as Haley reminds young George Shelby) the same. Haley sees all slaves, all the time, not as people but as profit or loss. Shelby sees them as such only when he is in serious money trouble, but this is a difference of degree, not kind. Shelby's selling of Eliza's child is, as an act, no less evil than Haley's selling of Lucy's baby to a passenger on the Ohio riverboat, although the consequences are quite different. Shelby tells Haley that he will not consider selling Eliza into sexual slavery (not because he knows this would be wrong, but because his wife would never forgive him), but he scarcely hesitates to sell little Harry into what he knows is almost surely the same fate.
Throughout the novel, Stowe shows slavery as hurtful and harmful to individual slaves, physically and emotionally; she knows this will have a wrenching emotional effect upon her audience. Thus Harris's forcing George to kill his own dog, Eliza's painful and frightened flight away from the only home she remembers, Tom's heartbroken farewell to his wife and children, the separation of old Aunt Hagar from her last and only child, the brutal whippings endured by George, Prue, Tom — all of these incidents are effective in showing the institution as it creates pain.
But even more terrible, from Stowe's point of view, is its creation of moral injury. Beginning subtly, with her sketch of Black Sam on Shelby's farm, whose morality is compromised by his need to promote himself as a favorite to his master (making him willing to help capture Eliza and her son if need be), Stowe shows slaves whose moral and spiritual soundness is damaged or destroyed by what happens to them. Lucy, on the steamboat, commits suicide despite Tom's efforts to help her. Old Prue, in New Orleans, tells Tom she would rather go to hell than to a heaven where white people are; she is in despair, and she dies in this condition. Cassy, too, is in despair; she has committed murder and attempted murder, and she is ready to kill Legree. St. Clare's slaves, who have learned to see themselves as materialistically as their owners see them, are morally degenerate. The thousands of slaves sold into sexual slavery or used sexually by their owners are in grave moral danger. Children like Topsy, raised to think of themselves as objects, of no value, are being set up, through absolutely no fault of their own, for morally barren lives — and worse, for lives of sin: the choice of evil over good.
Modern readers, who may have relatively little awareness of or respect for moral and spiritual matters, in comparison with matters physical and emotional, are apt to see these dangers as less important than they seemed to Stowe and her nineteenth-century audience. But to Stowe, the moral impact of slavery was among its chief evils, and to object that the moral responsibility belonged to the masters, not the slaves — who after all could not help themselves — would be a way of saying that these slaves were not adult human beings, people whose moral choices were their own to make. Yes, Stowe would agree that the masters were to blame for giving them nothing but difficult choices; but the moral choice for any action (or inaction) is made, she would say, by the person himself or herself. Slavery is evil because it attempts to reduce to objects people who cannot be so reduced.
The slaves themselves, of course, are not the only people whom slavery attempts to reduce and whom it thereby injures. The most obvious example of a slave owner destroyed by the institution is Marie St. Clare, whose narcissism is a result of her having been raised from infancy to believe that she is a superior kind of being. Marie's sadism is a natural result of her condition, as is her unhappiness: "If these people are not real, as I am real," Marie tells herself on one level, "then I may hurt them without guilt." But at the same time, she knows they are as real as she is — or that she is as unreal as they are — and this self-contradictory knowledge is the source of the imaginary pain she does feel and the very real pain she cannot. According to Stowe's lights, Marie is as doomed as Legree to a hell after death; meanwhile, she is in a kind of hell on earth — a different one from the one she subjects her slaves to, but a hell nonetheless. St. Clare himself, despite his role as one of the novel's chief spokesmen against slavery, has been morally injured by it; having found it easier to accept the institution than to combat it, he rejects spirituality for both his slaves and himself. Shelby and his wife are both shallow, callous people — as they must be if they are to continue owning slaves. At the physical center of the novel is St. Clare's nephew, the 12-year-old Henrique, shown to be potentially a kind, loving human being, who is being carefully trained and educated to be as meaningless to himself as Topsy, as soulless as Marie. Even Legree, who as the personification of the institution is an almost inhuman villain, is someone whom slavery has allowed and encouraged to become truly evil, morally dead before he has died physically.
Only Tom loves Legree. This is the irony at the heart of the novel, the key to its thematic conflict. In order to understand what it means, we need to remember, first, that Legree personifies slavery, which is evil precisely because it reduces (or attempts to reduce) human beings to property — material objects devoid of spiritual existence and value. But slavery cannot actually objectify human beings; Christian love (Christ's love, from which, Tom says in his dying words, we are inseparable) is stronger. Tom is able to separate slavery from its personification in Legree, to "hate the sin but love the sinner." By being able to love Legree, to forgive him (a spiritual feat that is not easy even for Tom to achieve, one that he calls "a victory"), Tom is able to triumph over the evil that Legree personifies.
We need also to remember that Tom does not love Legree in the material sense (in which Topsy, for example, says she loves candy), nor yet in the emotional sense that Tom loves his children. He does not love him, as some readers have apparently thought, in the sense that a prisoner of war begins to "love" (really, to depend upon, to "identify with" in self-protection) his captors. Tom loves Legree as, according to the Gospel of Matthew (5: 44), Christ counseled his listeners to "love their enemies"; he forgives Legree as, according to the Gospel of Luke (23: 34), Christ as he died forgave the men who had crucified him. According to Christian doctrine, this kind of love is the respect due one's fellow human beings, not because they have earned it but because they are human beings. It is precisely the kind of love that slavery denies when it denies people their humanity and views them as objects, commodities to be bought and sold, property to be used in the gaining of profit.
The theme of Uncle Tom's Cabin, then, is the conflict between the evil of slavery and the good of Christian love. Eva, symbolic of this sort of love, is killed (mythically) by slavery, but like Tom, she triumphs over death and thus over evil. If Tom were willing to hate Legree, to deny him Christian love, still he would not necessarily be willing to kill the man, as Cassy asks, or to allow Cassy to kill him, or to run away along with Cassy and Emmeline and leave Legree's other slaves to face the consequences — nor, of course, would he necessarily be willing to give up Cassy and Emmeline's hiding place to Legree; the difference, however, would be one of degree, not of kind. Tom too, then, dies but triumphs over death — as, we are meant to understand, do the two men who have carried out Legree's orders to kill him, saved from evil by Tom's dying love and forgiveness. Legree does not so triumph; in spite of Tom's prayers, we are told that he continues to choose evil and at last dies in it, physically as he has spiritually — and no doubt luckily for the popularity of the novel, whose readers might have protested had the villain been allowed to escape his just punishment in the afterlife.