Alexis Karenin, Anna's husband, is a cold fish. He's got wealth and excellent social and professional connections, a wife whom everybody adores, and a high-spirited son. But none of these things seems to touch him personally. Karenin lives according to a strict schedule of work, dinner parties, and reading, with evenings spent in philosophical (but not emotional) discussions with his wife.
All the while, it never occurs to him to think that the woman he sleeps next to at night has an internal life of her own. He just assumes that everything in his life is going like clockwork. Tolstoy is interested in what happens when this honest, upstanding, but heartless man suddenly realizes that the people around him are not simply cogs in the machine that is his life.
Karenin's coldness is perhaps another example of how things can go morally wrong for people not raised in a loving family situation (for another example, see Vronsky's "Character Analysis"). Karenin is an orphan with a wealthy and well-connected uncle (5.21.9). As a boy, he had great opportunities for doing well in school, but he didn't have much of an emotional environment. And now he's successful as an official in the Petersburg court, but lacking a substantial emotional life.
We might be able to explain what makes Karenin the way he is, but Anna Karenina isn't preoccupied with origin stories. What matters are the consequences of his actions, as we see his coldly ambitious self begin to fall apart once he can no longer take Anna Karenina for granted.
We know from the outset that Karenin has excellent professional connections because Oblonsky (Karenin's brother-in-law) has his official job mainly through Karenin's influence. What seems to be the cost of Karenin's professional success, though, is his personal life: he just has no feeling for human interactions that go beyond the give-and-take of everyday work life.
Karenin is slow to notice what the rest of society sees immediately—that Anna and Vronsky are head over heels for one another—because it genuinely never occurs to him that his (much younger) wife would act outside the social rules laid down for her (2.8.4).
And when Karenin finally does catch on in Part 3, after Anna has confessed all in the carriage ride away from Vronsky's steeplechase, does Karenin yell at Anna for cheating on him? Does he demand that she drop Vronsky? Does he decide to challenge Vronsky to a duel, which Vronsky and the rest of high Petersburg society expect of a man in his position? Not at all. After thinking about it for a while, Karenin decides it would be too painful to have a public divorce. All he wants is for Anna to act like his wife, even if they're living separate lives (3.23.21). The form of marriage is all that matters to Karenin here, not the feeling behind it:
"Very well! But I expect a strict observance of the external forms of propriety till such time"—his voice shook—"as I may take measures to secure my honor and communicate them to you." (2.29.42)
Slowly, though, Karenin's hard professional shell starts to break down. In Part 4, when he sees a lawyer about a potential divorce, he realizes that the lawyer is laughing at him, and seems to be genuinely pleased at Karenin's suffering. Karenin keeps noticing this throughout the rest of the novel:
But as time went on, he saw more and more distinctly that however natural the position now seemed to him, he would not long be allowed to remain in it. He felt that besides the blessed spiritual force controlling his soul, there was another, a brutal force, as powerful, or more powerful, which controlled his life, and that this force would not allow him that humble peace he longed for. He felt that everyone was looking at him with inquiring wonder, that he was not understood, and that something was expected of him. Above all, he felt the instability and unnaturalness of his relations with his wife. (4.19.3)
Even his old work buddies are taking gross pleasure at the knowledge that Karenin's wife is cheating on him. Karenin's shame and humiliation at being openly known as a cuckold (a man whose wife has cheated on him) starts to erode his perfect social position.
In fact, later in the novel, it turns out that the weakness of Karenin's married life, and the fact that he's now the laughingstock of Petersburg, has ruined his career. His work cronies all laugh behind Karenin's back that he thinks his career is still going well. But, while Karenin's current job is safe, everyone else knows that he will never be promoted again. All of his careful, rational career building seems to be undercut by the fact that he never took his wife's feelings into account. His inability to handle her adultery with any passion or interest has, in the end, been a professional liability. He still has lots of plans and ideas... but no one's listening to him anymore:
He felt that he could not endure the weight of universal contempt and exasperation, which he had distinctly seen in the face of the clerk and of Korney, and of everyone, without exception, whom he had met during those two days. He felt that he could not turn aside from himself the hatred of men, because that hatred did not come from his being bad (in that case he could have tried to be better), but from his being shamefully and repulsively unhappy. He knew that for this, for the very fact that his heart was torn with grief, they would be merciless to him. He felt that men would crush him as dogs strangle a torn dog yelping with pain. He knew that his sole means of security against people was to hide his wounds from them, and instinctively he tried to do this for two days, but now he felt incapable of keeping up the unequal struggle. (5.21.5)
In a sense, then, the novel punishes Karenin's lack of feeling by taking away the career that dominates his emotional life. Yet, at the same time, it's not just punishment: we see that Karenin's social and professional crisis does open up a new emotional life for him. The fury that he feels at Anna gives way to forgiveness, and then to love for her daughter, Annie. His cold shell of the first third of the book is broken (or at least dented), after the brutal reminder that Anna does, indeed, have feelings of her own.
In Part 5, Chapter 21, Karenin realizes that he had never thought he needed friends once he had a career and a "perfect" wife. So, in this moment of great crisis, he has no one to talk to, no buddies who can advise him what on to do. But, by the end of the novel, Karenin has other people in his life: Seryozha, Annie, and possibly Countess Lydia. Maybe he's still not the greatest guy in the world, but over the course of the novel, Karenin has developed from a shell of a guy to a character with some depth.
There are two kinds of religion in competition with one another in Anna Karenina—"real faith" and piety for the sake of proving you're better than everyone else. Let's look at both kinds of religion with respect to Karenin's character.
Karenin isn't too religious at the beginning of the novel. Religious faith doesn't seem to fit into his rational approach to life. But Karenin has a transformative experience when he thinks Anna's going to die in childbirth. He suddenly realizes that 1) he had been wanting her to die, and 2) he knows that that was bad, and that he needs to forgive her. And here's the interesting thing—he does forgive her. He forgives both Anna and Vronsky wholeheartedly, out of Christian faith in the importance of personal humility. (4.17.54)
This is probably Karenin's best moment in the novel. At Anna's side, he really shows up Vronsky, who feels ashamed at Karenin's generosity. For a time, it seems that Karenin changes for the better. He knows that the society he values disapproves of him, that all of his acquaintances think he should've challenged Vronsky to a duel, divorced Anna, or done something other than trying to keep up appearances. But Karenin's brief moment of illumination gives him the strength not to care about that. He tells Vronsky:
[Karenin:] "But I saw her and forgave her. And the happiness of forgiveness has revealed to me my duty. I forgive completely. I would offer the other cheek, I would give my cloak if my coat be taken. I pray to God only not to take from me the bliss of forgiveness!"
Tears stood in his eyes, and the luminous, serene look in them impressed Vronsky.
You may trample me in the mud, make me the laughing-stock of society, I will not abandon her, I will never say a word of reproach to you. (4.17.52-54)
Karenin's Christian willingness to forgive (Karenin uses Jesus' instructions to his followers to turn the other cheek in the Gospel of Matthew; for more on this, see our section on "What's Up with the Epigraph?") is genuine while it lasts. But it doesn't last forever.
The thing that spoils Karenin's epiphany, which is otherwise just as important as Levin's, is that he gradually returns to the disapproving society that surrounds him. Slowly, he remembers that his colleagues despise him and he has no friends. He feels lower than everyone around him again, because Anna has publicly humiliated him. And even though Karenin tries, he can't hang on to the calmness that this one brush with God gives him. (In particular, see Part 5, Chapter 25 on this experience.)
Levin gets to have his epiphany in the countryside surrounded by his family for support. But Karenin's realization of the power of forgiveness is more fragile because he doesn't have the emotional support to ignore society the way Levin can. So what does he turn to instead? His exploitative, hypocritical friend Countess Lydia, and her fake religious sentiments.
Countess Lydia believes in two things. First, she believes that once you accept God as your salvation, you can do no wrong, because all of your sins have already been forgiven. And she believes in the séances and conversations with the afterlife that were popular at this point in the 19th Century. (Be sure to check out Countess Lydia's "Character Analysis.") What Karenin finds appealing about Countess Lydia's brand of religion is that first bit: that no matter what you do in life, if you accept God, your deeds don't matter.
To Tolstoy, this kind of religion is dangerous for two reasons. It convinces you that you are always better than everyone else, because you have God on your side. And second, it gives you permission to do whatever you want. If you've already been saved, you won't have any incentive to do good works or to be charitable. According to Tolstoy, this kind of religion is a recipe for complacency. But it's exactly what Karenin wants: a religious faith that proves that he's better than anyone else.
In his life in Petersburg without Anna, Karenin is alone and humiliated. He's just waiting to latch on to someone or something that will make him feel better about himself. And so, when the holier-than-thou Countess Lydia comes around to tell him that everything bad that's happened is Anna's fault, Karenin quickly takes it all in. In Part 5, Karenin's at a low point in his life—he's starting to lose the faith he won at Anna's supposed deathbed. When Countess Lydia offers him a religion that makes him better than all those society people who make fun of him behind his back, he eagerly converts.
The thing that's really tragic about Karenin's weak acceptance of this fake religion is that he had a brush with genuine religion when he decided to forgive Anna. So in his heart of hearts, he knows that Countess Lydia's form of Christianity is hypocritical and untrue. But he clings to it anyway because he needs something to believe in that will support his ego. So Karenin tries to be a better man, but Petersburg society manages to make sure that he doesn't get to stay that way.