Jerry Cruncher's secret nighttime activity is grave robbing. Under the cover of darkness, he digs up fresh corpses and sells them to medical schools so that the students can use them in their study of anatomy.
Cruncher's activities reinforce two themes that are central to the novel. First of all, he is literally a "resurrection man", removing the deceased from their place among the dead and returning them to resume their existence among the living. Dickens uses the image of imprisonment freely in the novel as a symbolic sort of death. Dr. Manette is the most obvious character who experiences "resurrection", having been "recalled to life" after being held captive for eighteen years. Charles Darnay also experiences death and resurrection twice, when he is imprisoned but eventually released. In a larger sense, the theme of death is exemplified by the anarchy and hatred that consumes the masses during the French Revolution. The Charles and Lucie Darnay, Dr. Manette, and especially Sydney Carton are resurrected from this atmosphere of death through their love and self-sacrifice.
The other theme that is reinforced through Jerry Cruncher's nighttime activities is the idea that things are not what they seem to be. Cruncher by day is a respectable citizen, an employee of the prestigious Tellsons' Bank. By night, however, he is a criminal of the lowest kind, a man who robs graves. In a like manner, Charles Darnay aspires to be nothing more than an ordinary, hardworking British citizen, while in reality, he is the heir of the Evremondes, one of the most notorious families of the French aristocracy. In another example, Sydney Carton appears to be no more than a crass, degenerate individual, but he turns out to be a hero, giving his very life in an unselfish sacrifice of love.
Jerry Cruncher who calls himself "an honest tradesman" comes home with mud on his boots and his wife desperately prays for the salvation of his soul as he tries to sleep. As comic relief in this melodramatic novel, Cruncher uses euphemisms--a common feature of lower-middle-class life in London--that create respectability for digging up buried bodies while prayer is degraded to "flopping." In this digging up of bodies, Jerry also turns into parody the theme of resurrection in "A Tale of Two Cities."
Dickens's novel is a narrative replete with pairs: Carton and Darnay resemble each other, Mr. Lorry and Dr. Manette are similar in age and both have been prisoners--Manette of the Bastille and Lorry of its parody, Tellson's Bank; Paris is paired with London, Miss Pross the sturdy servant with Gabelle, the caretaker of the Evremonde estate; the Marquis St. Evremonde with Mr. Stryver; and Jerry Cruncher as an inversion of Sydney Carton. For while Jerry "resurrects" bodies for an irreverent purpose, Carton's irreverent body will later receive the ressurrection of the soul.