Coming of Age
Tris, Tobias, and their friends are forced to cope with an entirely new reality upon leaving the city to see what lies beyond its walls. Their entire livelihood -- the factions, the city's enclosed walls, Divergence, etc. -- all of it became a hoax when they reached the Bureau of Genetic Welfare. They were told by David that they were merely part of an experiment, and that their existence was a means to an end. All of a sudden, these characters were forced to adapt to this knowledge.
It's almost as though the group is forced out of childhood and into adulthood in the span of a couple of hours. None of them was ready for what the outside world would hold. They couldn't have possibly prepared themselves for what they found out. Yet they had to learn to live with their new reality. Expanding their worldview, adapting to new information, and embracing the curiosity that drove them outside the city, the group comes of age in their journey beyond their home.
Dealing with Guilt
The characters in this story are ridden with guilt. Tobias feels guilty for his role in the plan that resulted in the explosion that put Uriah into a deathly coma. Tris still feels guilty for killing her friend Will -- so guilty that she has trouble firing a gun. Caleb feels guilty for not defending his sister, choosing to deliver her to what was almost her execution at the hands of Jeanine Matthews.
Instead of letting their guilt rule them, these characters learn to live with their guilt. Tobias decides to enter the city to tell Uriah's family about what happened to him. Caleb attempts to sacrifice his own life by entering the Weapons Lab, and Tris (having apologized long ago) tries to move on from her past. Each has their own way of dealing with guilt, but they all attempt to achieve the same goal: to live with this guilt. Often guilt can incapacitate a person, but the characters in this story must keep living and fighting, or else they would lose their lives.
Embracing Uncertainty
Tris and Tobias exited the city having no idea what they would find beyond its limits. This was scary, yet their group left the city anyway. Though they don't like what they find at the Bureau, their curiosity reigns. The group continues to want to understand what is going on at the Bureau, despite it being such a foreign and scary place to them.
Later in the novel, both Tobias and Tris agree to venture into the fringe (on separate occasions). Tobias goes with Nita to meet Mary and Rafi, while Tris goes with George and Amar on a surveillance mission. Tris and Tobias had only heard about the horrors of the fringe, and they were curious to see the place for themselves. Embracing their uncertainty, the two both stepped out of the safety of the compound to see what the fringe was truly like.
The same sort of situation arises when Tris volunteers to enter the Weapons Lab instead of Caleb. She doesn't know if she'll survive the death serum; in fact, she accepts that she may not, entering yet another void of uncertainty. At the same time, Tobias does the same when he chooses to talk to Evelyn instead of Marcus. He doesn't know which parent will be more receptive to his attempts to stop war from breaking out in the city, but he makes a decision and runs with it.
Fighting for Your Loved Ones
This theme is important from the beginning of the novel, as Tris constantly remembers how her parents (especially her mother) gave up their lives so that she and Caleb would have the chance to continue living. Knowing this, Tris reads her mother's journal, and her resolve to fight for her loved ones only magnifies.
First and foremost, Tris sacrifices her own life at the end of the novel for the good of her friends and everyone in the city. She enters the Weapons Lab in Caleb's place -- knowing that she could never let him walk into his own execution. Despite all of the wrongs that Caleb had done to her, he was still her brother, and she would always love him. She would never be able to live with herself if she didn't take his place.
Tris also fights for her loved ones when she stops Nita from entering the Weapons Lab. If Nita had succeeded, she would've released the death serum, killing hundreds of people in the compound. Nita had no regard for whom she killed -- and Tris knew that the death serum could have killed many of her friends.
Similarly, when Tobias breaks Caleb out of his cell in the Erudite compound before they leave the city, he is fighting for his loved one: Tris. He knows that Tris couldn't live with herself if Caleb died while they escaped the city, so he got Caleb out so that he would live. Even though Tris didn't ask him to do this, she is grateful.
All of the characters in the group that exits the city fight for each other. They lean on each other, working together to venture through the unknown that is the outside world.
Identity
The group from Chicago struggles constantly with a crisis of identity outside the city. They have each come to identify with the faction from which they came. Cara and Caleb are Erudite, leaning on their intelligence and rationality more than anything, Christina and Peter are Dauntless, knowing that they are brave and can face their fears better than anyone, and Tobias and Tris have come to identify as Divergent, not quite fitting into one of the factions, but thriving still. The factions and their implications are all that mattered to these characters for the majority of their lives. When they get to the Bureau, they are told that the factions were meaningless, only part of an experiment.
Suddenly, their identities mean nothing. Then, making things only worse, many of the characters are told that their genes are damaged. They're told that they have limitations, making them less than people with pure genes. Tobias, no longer able to identify as Divergent, has no idea what to think of himself. Cara and Caleb are even more at a loss in this new world, as the revelations that the outside world brought are almost too much to think about rationally.
Learning that the world in which you live is a lie brings about an overwhelming shock to the characters. They have to cope with these facts, changing their worldviews and altering what they come to identify by in the process. Many of the characters have nothing to lean on but each other.
The Power of Forgiveness
Tris and Tobias constantly find themselves at odds with each other. At one point in the story, when Tobias refuses to listen when Tris tells him she doesn't think they should help in Nita's plot to undermine the power of the Bureau, Tris ends up angry at Tobias when she was right. Nita had been lying to them -- saying they were going to steal memory serum, when they were really trying to steal death serum -- and the plan resulted in Uriah's deathly coma. Tris and Tobias don't talk for days, but it is eventually her capacity to love and forgive him that mends their relationship. If not for forgiveness, slight wrongs and misdoings would ruin the friendships that the group from the city has. In such an unknown place as the Bureau, they cannot hope to survive without forgiving each other and sticking together.
Later in the story, forgiveness comes back into play when Caleb is preparing himself to sacrifice his own live to reset the Bureau officials in the Weapons Lab. Tris knows that he is only doing this to get away from his own guilt; he can't live with himself. She tells him that she forgives him, and she forces him to let her take his place in the Weapons Lab. If she hadn't done this, Caleb probably would not have succeeded in setting off the memory serum. More importantly, Tris wouldn't have been able to live with herself had she let Caleb die.
One last example of this theme occurs between Tobias and his mother, Evelyn. Tobias enters the city prepared to reset the memories of one of his parents in order to stop the city from entering a civil war. Instead of resetting his mother, he tells her that he will forgive her, that he'll be her son again, if she stops trying to rule the city. She agrees, wanting nothing more than reconciliation with and forgiveness from her son.
The Solace Found in Love
Tris and her friends feel utterly alone in the world outside the city. They are uncertain and afraid, and the only people that they have to rely on are their friends. As their old home edges closer and closer to a full-on civil war, as the characters find out that their life was nothing but an experiment, as the characters deal with learning that they are genetically damaged, they cannot physically cope alone. The love forged between friends and comrades is stronger than one might think. The characters know that they aren't really alone, as their friends are going through the exact thing that they are.
The story also elevates the love found between family members. Tris reads her mother's old journal, which reveals that her mother and father fell in love shortly after she entered the Chicago experiment. The two had rebelled and joined Abnegation together. Similarly, Tris eventually realizes that the love between her and Caleb has no bounds. She decides to lay down her life for him, knowing that it's what her parents would have done.
Most important of all is the love between Tobias and Tris. They are soul mates, ready to face anything as long as they have each other to rely on. In any moment of uncertainty, the two often find each other. All they have to do is hold each other, kissing lightly, to forget everything that is happening in the Bureau. Love blocks all the bad in the world.
