The banker's money (symbol)
The millions of the banker are used as a symbol for the value of 15 years of the young lawyer's life, which he will spend imprisoned, with no human connection. They are also a symbol for the greed of the young lawyer, who is willing to sacrifice 15 years of his life, either to prove his point in the argument, or for the money. The case could be made for either, though at the end of the story, he refers to the money as a dream of paradise, enlightened by his time in solitude.
Permanent change (motif)
When the banker makes his case against capital punishment, he argues that the government does not have the right to take away what they cannot give back: i.e. someone's life. This motif ironically resurfaces when he himself considers killing the lawyer to absolve himself of the impending 2-million-ruble debt. We can also see the motif at work in the lawyer: despite not being permanently killed, his time in solitude does permanently transform him into someone who has transcended the banker's own obsession with material wealth.
Books (symbol)
The lawyer, during his imprisonment, voraciously reads a variety of books. He uses them to replace the human interaction and stimulation that he would have otherwise had in the real world. To him, they become his world. In this way, then, their words and worlds become symbolic of his entire realm of experience.
The Gospel (symbol)
The lawyer studies the Gospel for a whole year, whereas in other years he reads up to 600 books. This symbolizes the importance of God in the lawyer's quest for knowledge and enlightenment. It also gives us insight into the lawyer's mindset: he is grappling for faith, the only thing left beyond knowledge.
Piano (symbol)
The lawyer often plays the piano during his first year of captivity, but he leaves it silent in the second. This symbolizes his shifting mindset, progressively turning inward in his solitude.
