Augustine St. Clare, father of Eva and brief owner of Tom, is perhaps the most contradictory character in Stowe’s novel – he sees what’s right but fails to do it. In this, he reminds us of the Biblical Paul, who said "I do not understand what I do. For what I want to do I do not do, but what I hate I do" (Romans 7:15). Or, as St. Clare himself, describes it, his life is "a contemptible non sequitur" – it doesn’t follow from his own opinions (19.98).
A Louisiana gentleman with aristocratic heritage, St. Clare is intelligent enough to recognize the evils of slavery as an institution, but his mother’s early death and the failure of his first romance have left him emotionally and morally stunted. He won’t actively harm his own slaves, but he also hasn’t freed them. He won’t become a Christian largely because he’s afraid that, if he did, he’d feel morally compelled to take on the huge weight of the abolitionist cause:
St. Clare had never pretended to govern himself by any religious obligation; and a certain fineness of nature gave him such an instinctive view of the extent of the requirements of Christianity, that he shrank, by anticipation, from what he felt would be the exactions of his own conscience, if he once did resolve to assume them. For, so inconsistent a thing is human nature, especially in the ideal, that not to undertake a thing at all seems better than to undertake and come short. (28.4)
In other words, St. Clare knows at the back of his mind or at the bottom of his heart that Christianity has real force and that slavery is wrong. But he’s afraid of how difficult it would be to act on his convictions, so he buries them and rationalizes them away.
St. Clare excuses his failure to act against slavery to his harsh, slave-owning twin brother, Alfred, by claiming that one man can’t really make a difference. But Stowe’s readers know that a difference can only ever be made by one person. She even gives us an example of how much one man can do even if he seems powerless – Uncle Tom himself, whose quiet dignity and faith affect everyone around him. (Even Simon Legree – maybe he isn’t converted, but he is affected.) St. Clare acts helpless, but his own slave shows him up.
Basically, St. Clare is unwilling to spend his life doing the right thing, even though he knows what the right thing is. He’s too interested in making his own life as easy as possible. He’s perfectly willing to point out the problems with slavery, but also the problems with the "easy" solutions offered by the North – represented in his own household by his cousin Miss Ophelia. St. Clare recognizes that he’s complicit in the problem because he hasn’t freed his slaves, but he also recognizes that emancipated slaves would still have huge challenges to overcome – such as their lack of education and the strong racism of North and South alike. St. Clare is the original critic: he loves poking holes in other people’s ideas, but doesn’t actually have any of his own.
When St. Clare’s precious daughter Eva dies, it seems to work a real change in his attitude. He promises Eva that he will free Tom and that he will devote his life to exhorting others against slavery. In short, he’ll become the powerful abolitionist orator that he always knew he ought to be, and he’ll try to lead his society through a moral revolution.
Unfortunately, in a freak accident, he dies shortly after Eva, and his selfish wife Marie sends all the St. Clare slaves – for whom he made no legal provision in his will – on the auction block. St. Clare’s revolution is short-lived.