The success of A Tale of Two Cities can be attributed to Dickens's artful setting of a touching human story against the background of the world-shaking events of the French Revolution, and to the themes related with these events. Among these themes, one of the most important is the theme of sacrifice, as the way to self-fulfillment.
An accompanying are the themes of retribution and human loyalty - kind and sympathetic in the case of the Manettes, father and daughter, and Miss Pross; appalling though understandable in the case of Madame Defarge, who can never forget what the Evrémondes did to her family. Another theme is the resemblances and parallels Dickens wants us to see between London and Paris. The two cities represent opposed mindsets that are personified by contrasting female characters.
Dickens refers first to the London carts and coaches, in which “pale travellers set out continually on a violent passage into the other world” from the criminal court and prison of Old Bailey (Dickens, ii 2). Later, before he depicts the mob in Paris, he gives us a London crowd, which “in those times stopped at nothing, and was a monster much dreade” (Dickens, ii 14).
Dickens’s most memorable characters tend to be the eccentrics, the droll fellows. In A Tale of Two Cities there are few of these: Miss Pross and Jerry Cruncher are the two most notable. As a contrast to them there is the pushing Stryver; he is not really entertaining.
The rest of Dickens’s characters do not hold much of the reader's interest. Thus, Sydney Carton, Charles Darnay, Lucie Manette, the good Doctor Manette, and Jarvis Lorry all seem relatively normal people, who in other circumstances would not be very interesting.
The same might even be true of the Defarges, husband and wife. Had they not had a revolution to fight, their lives might have been routine, and not worth investigating. But in this novel, the driving force is an impersonal one. Its impact on character is felt most strongly when we consider the two principal antagonists: Sydney Carton and Madame Defarge.
Sydney Carton is a case of a spoiled man who has somehow lost his nerve and his self-respect and bitterly knows it. He gets the chance to do a noble thing and, in doing it, redeems his wasted life. But, had there been no such opportunity, we must suspect that he would have gone on in his downward track, drinking more and enjoying it less, and at some point being cast off by the now affluent Stryver - the man who has used him to his own great benefit - when he needs him no longer.