Pierre is very much regretting his life choices and rightfully blaming is own short comings for them:
So he does the obvious and joins a cult. The Freemasons to be specific. But Christina, you say, how can you be sure they are a cult? Well, how about this:
In the book the rituals Pierre gets subjected to are endless and I had to wonder just how naive Pierre is not to be suspicious of the high amount of pseudo spiritual bs combined with the frequent demands for donations. Poor Pierre is just desperately wanting to be a good person, he happily throws money at anything that might get him there and the Freemasons with their promise of building a Brotherhood of Men hit the jackpot here. In his defense, he does not only submit himself to rituals or donates money, he actually (finally) tries to use his position as a count to improve the lives of people he holds power over. I had really looked forward to this part in the book, as the TV series only deals with his attempts to implement reforms in one scene. In this scene is is implied that the reforms are inefficient because of his naiveté (or stupidity, as I would say):
Interestingly, in the book, it is more complicated than that. Pierre has obviously no idea how to run his estates. He is also very much aware of this fact. He knows he should sit down and learn how things work if he wants to make effective reforms, but he is simply too lazy and easily distracted to do so. Instead he relies on the overseers of his estate to advice him, who cheat him out of a lot of money, and actually make the lives of his serfs worse. Pierre willingly lets himself be fooled, because it allows him to feel better about himself without actually having to do the hard work of changing.
Nikolai on the other hand does. He starts living within his means, manages to saves his army wages and pays back his dept to his father. Which the TV series does not mention AT ALL. Nikolai finds meaning in the simple life and the camaraderie of the soldiers. He is also still very much in love with the Tsar (who Tolstoy really wants you to know is handsome). After already having been disillusioned by war, he now becomes disillusioned with the whole military system. The soldiers are left to starve and in desperation Denisov seizes provisions meant for another regiment to save his men. He gets court-martialed and Nikolai tries to get him a pardon from the Tsar. He witnesses a meeting between the Tsar and Napoleon and is aghast on how the Tsar treats him as an equal:
Then some random Russian soldiers get the (french) Legion of Honor as an (empty) gesture, while the Tsar tells Nikolai he cannot do anything about Denisov. During this whole adventure Nikolai meets Boris, who I have mainly ignored. Boris's story is parallel to Nikolai. They both start at the low ranks, but while Nikolai refuses to use his connections and has no head for politics, Boris is rising rapidly through the ranks.
Andrei decided to become even more insufferable by adopting nihilism. Nothing matters now, only his family and he is going to spend the rest of his life contemplating the meaningless of all existence. As this is high literature, we of course need SYMBOLISM:
See the tree? Guess what he represents? And you won't believe what happens once Pierre comes to visit and bombards him with all his newfound enthusiasm about the Freemasons and helping mankind until even Andrei has to admit that maybe life is not meaningless after all:
The conversation between Pierre and Andrei is actually really lovely and the TV series brings out the cinematography to support it:
I can now almost forgive them for editing the series in a way that makes it look as if meeting Natasha is the reason he changes his outlook. In the book it is very clearly Pierre's influence (more about this in the next book) and he falls in love with Natasha AFTER his changed attitude makes it possible for him to be open to the possibility of love.