I think the main symbolic image from the story is money, specifically the two million rubles.
When the story starts out, the debate is about whether it is better to die quickly (death penalty) or to die slowly (life in prison). The banker believes the former, but the lawyer believes that any life is better than no life.
"The death sentence and the life sentence are equally immoral, but if I had to choose between the death penalty and imprisonment for life, I would certainly choose the second. To live anyhow is better than not at all."
The question is quickly shifted to a question of worth. Is a man's time worth more, or is 2 million rubles worth more? It's basically a question of how much a person's time is worth. To the banker, his time is worth more. To the lawyer, the money is worth more.
All of that is flipped around by the end of the story though. The banker is next to broke, so the two million is deeply important to him. On the other hand, the lawyer doesn't want the money anymore. The two million rubles is symbolic of each man's values and how those values shift around over the course of the story.