Christianity is an important theme throughout the novel. For instance, Uncle Tom's Christianity is a foundational part of who he is. It drives his actions and enables him to retain his dignity, courage, and humanity in terrible situations. Stowe compares it to the morality of a so-called Christian nation which allows the horror of owning slaves. She especially compares Tom's Christianity to the evil, un-Christian behavior of Simon Legree, who feels no pity toward his slaves and controls them through savagery and violence. Legree would rather kill his slaves off through overwork and replace them than treat them with minimal decency. Throughout the chapters on Legree's plantation, Stowe shows that nobody should be owned by a man of Legree's temperament. She illustrates as well that it is ludicrous that a man of Tom's moral character should be owned by a drunken, superstitious man on the basis of race.
Mrs. Shelby, as do many of the moral characters in the book, uses Christianity to fight slavery. She does this by trying to persuade her husband not to sell Eliza's four-year-old son away from his mother. Mrs. Shelby says,
I have talked with Eliza about her boy—her duty to him as a Christian mother, to watch over him, pray for him, and bring him up in a Christian way; and now what can I say, if you tear him away, and sell him, soul and body, to a profane, unprincipled man, just to save a little money? I have told her that one soul is worth more than all the money in the world; and how will she believe me when she sees us turn round and sell her child?—sell him, perhaps, to certain ruin of body and soul!
As you look through the book, you should be able to find many more examples of Stowe exploring religious themes.
There are a number of very important religious points that Stowe uses to show the evils of slavery.
First, it is important to note that the context of the novel is rooted in Christianity. Also the novel was published in a Christian culture. Therefore, there is a huge blind-spot when it comes to the Christianity of those who did not fight against slavery. The good masters of the novel are no exceptions. Their moral failings are clear in that they did not speak against slavery.
Second, Eva and Tom are the two most morally flawless characters in the book. They are clear examples of Christ. This can be best seen in that they both died and gave life to others. Eva's death leads to St. Clare's conversion to faith. And Tom's death leads to the escape of Emmeline and Cassy. These points are made clear in that Ophelia says that Eva looks like Jesus, and Tom is compared to Christ carrying the cross.
These points would not have been missed by those of Stowe's day.