The main idea of A Tale of Two Cities centers on transformation. Throughout the novel, both individual people and entire societies are transformed. However, transformation does not come without risk and sacrifice.
For instance, over the course of the story, Sydney Carton finds redemption for himself by learning to be more empathetic and moral and less selfish. This culminates in him making the ultimate sacrifice so that his formal rival, Charles Darnay, can live happily ever after with his former love interest, Lucie Manette. By doing so, Carton is transformed from the morose young man he was into a Christlike hero. The reader also experiences the transformation of characters like Doctor Alexandre Manette, who is "recalled to life" as he finds new meaning as a father and a free man after his time as a prisoner.
Other transformations occur on a broader scale. France, which had suffered under the regime of callous aristocrats, is transformed by way of a violent revolution. Certainly, sacrifices are being made in an attempt to create a more egalitarian and just country. However, unlike the individual sacrifices of people like Carton, Dickens makes the reader wonder if such destruction and bloodshed are justified as the liberators are transformed into oppressors. The question that remains is whether such revolutionary transformations are worth the terrible tolls that they inflicted on nearly everyone involved.
There are two main ideas in Charles Dickens’s A Tale of Two Cities. The first idea, or theme, is one of redemption and resurrection. The second involves the failure of revolutionary movements to ensure a more just political regime.
Dickens’s novel takes place in the period leading up to and including the French Revolution, a protracted and messy affair that included the infamous "Reign of Terror." The late eighteenth century was a period of enormous social and political transformation in France. The aristocracy that dominated France and that gave rise to the revolutionary movement that ultimately toppled it was thoroughly corrupt and remiss in its responsibility to the lower classes. The poverty that dominated much of French society, especially in Paris, was a breeding ground for violent sentiments directed towards the aristocracy, famously personified by the monarchy of Louis XVI and Marie Antoinette, both of whom would be executed by guillotine.
While the violence, chaos, and authoritarianism that characterized the French Revolution—developments that stood in stark contrast to the revolution against the English monarchy across the Atlantic Ocean in North America during the same period of time—represented the short-term failure of the ideals upon which the revolution was carried out, Dickens’s more important theme revolved around the characters in his novel. The drunken, seemingly worthless lawyer Sydney Carton emerges as the noblest of humans, sacrificing his life for those whose lives he deems of greater value.
Lest the reader miss the theme of resurrection inherent in Carton’s actions, Dickens has his character reference the life of Christ in his final moments on Earth. As the knitting women methodically and dispassionately count off the dead, Carton repeats the statement he has made previously,
I am the Resurrection and the Life, saith the Lord: he that believeth in me, though he were dead, yet shall he live: and whosoever liveth and believeth in me shall never die.
For greater emphasis, Dickens then observes,
They said of him, about the city that night, that it was the peacefullest man’s face ever beheld there. Many added that he looked sublime and prophetic.
Carton has gone to the guillotine in the place of Darnay, the repentant former aristocrat, because he believes it is the noblest of actions and will lead to his resurrection. While the subversion of revolutionary ideals is a theme that runs throughout A Tale of Two Cities, it is the redemption of the characters that is arguably the more important theme.
More than revolution or even romantic love, the main idea of A Tale of Two Cities is resurrection. Multiple characters are "recalled to life" in one way or another throughout the story. Dr. Manette is freed from the Bastille at the beginning of the novel and restored from his psychological trauma by the love of his daughter, Lucie. Jerry Cruncher (whose initials are meant to evoke Jesus Christ) is described as a resurrection man since he takes bodies from graves to sell them to medical students—one could say that he is using the dead for the sake of the living.
In the last section of the novel, Dickens's sense of resurrection becomes more corporate. Of course, there is the spiritual resurrection of Sydney Carton, brought about by his love for Lucie and his willingness to die in order to save her husband from the guillotine's blade. The novel also implies another kind of resurrection for Carton through Lucie's son, who is named in honor of him and likely to fulfill the potential Carton himself never did in his own lifetime. However, Dickens also alludes to the eventual resurrection of France itself. Carton imagines the nation rising from the bloodshed of the revolution and restoring peace in its place.