The main theme of the story is the representation of an idea embodied by two characters. In this story, the lawyer represents the people who appreciate life over material stuff and the banker represents people who prefer money and material stuff over life. This is also represented in a duality where prison or death are two sides of the same idea, in this case, that's the reason why the characters do the bet, to prove one another that death is better than prison and vice-versa. Chekhov in this story uses his characters to represent a concept, because both, the lawyer and the banker, have opposite ideas and actions. The lawyer changes and grows in reclusion while the banker thinks about killing the lawyer because he can't pay the bet.
In this case one of the devices that the author uses to develop the story is characterization. This tool in literature is used to highlight and explain details about a character and their thought-processes. The author explains the lawyer and the banker's behaviors to contrast them and explain the main idea of the text. The other device that Chekhov uses is the point of view which consist in demonstrate the opinions and feelings of the characters to let the reader know that they are opposite and represent two sides of the same idea, so in this case the lawyer is the character who feels good things in life are the simple things as reading and learning while the banker thinks that money is the priority in his life so he would kill in order to avoid the bet.
