Augustine St. Clare, Tom's third owner and the father of the novel's saintly child, is an odd and interesting character, an amalgam of traits that we finally find coherent and human. He is a "Byronic" hero, a thoughtful spokesman against slavery, and a reluctant (and at last repentant) materialist.
St. Clare's character contains a huge contradiction, in that he is a slaveowner whose way of life is sustained by the system he rejects morally and philosophically. This contradiction must somehow be explained, if we are to find him anything but a complete hypocrite, and Stowe explains it by showing him as a lazy man — physically and especially morally. This is understood to be a result of a traumatic experience in St. Clare's past: His heart was broken. If he had married his true love, it is implied, he would have lived in the North and opposed slavery more truly and effectively than his cousins, for he grew up with the system and hated it personally. But, alas, St. Clare was cheated and betrayed; he foolishly married Marie, who could probably not breathe without the help of slaves; and he begat little Eva, the image of his sainted mother and the light of his life. Thus, he has become cynical, knowing what is right but careless of the state of his own soul. His obligation to Eva keeps him from becoming entirely dissolute, and his moral despair allows him to live with the guilt of enjoying a comfortable life that is supported by owning slaves.
St. Clare also has the ironic self-knowledge that allows him to speak honestly against slavery despite being unable to reject its comforts for himself; he is like a principled vegetarian who, despite alternate amusement and self-loathing, cannot give up eating meat. His long conversations with Ophelia express many facets of the abolitionist arguments of Stowe's time, including Stowe's own disgust with the hypocrisy of the churches — which, St. Clare says, provide scriptural support for slavery because it is economically profitable, but would provide scriptural opposition to it if it suddenly became unprofitable. But St. Clare's personal opposition to the system that provides him and his family with a comfortable, not to say luxurious, life has itself more than a whiff of hypocrisy, with which St. Clare seems generally unconcerned — until first Eva and then Tom are able to shake his complacency. St. Clare has been satisfied with avoiding sins of commission but has not recognized, until very late in his life, that sins of omission are as deadly. He does recognize this at last, and he fully intends to right his wrongs — soon, any day now. Ironically, although his intention and Tom's prayers are apparently enough to gain entrance to heaven for St. Clare in the end, his habits of idleness and materialism (habits instilled by the practice of slavery) have doomed the slaves he ought to have freed, including Tom, to a living hell.
Only one is saved. Because Ophelia insists on having legal control of Topsy, this child alone avoids the general sale of slaves when St. Clare dies and Marie inherits his property.