In Dickens's London, the dialect of a person is an indication of that person's socio-economic class and, concomitantly, his level of education. In addition to his portrayal as a character of the lower class, Jerry Cruncher provides comic relief as his creative terms and "luminous idea" of calling himself the euphemism of "Agricultooral character," for example, is a digression from the seriousness of the plot at this point of the novel. Jerry's graverobbing also parodies the theme of resurrection.
On the other hand, Jerry's speeches provide an insight into the life "on the other side" as it were. His descriptions of his wife's "flopping" connotes his disrespect for prayer and his rationalization of his actions by employing such a euphemism. But, he also displays insight. For instance, in his explanation of the value of his "agricultooral character," while Jerry explains that the doctors need bodies for scientific progress and they make money as a result, he makes only "fardens." Pointing to the hypocrisy of the upper class, Jerry cites his wife's "flopping" and prayers while no gentlewoman married to a doctor prays for any of the cadavers on which their husbands work.
Jerry demonstrates logical reasoning, too, as he creates a strong argument against Mr. Lorry's dismissing him as a messenger for Tellson's Bank as he explains that his son, too, sits upon the stool outside the bank and needs employment so that his father will not do more wrong.
Upon that there stool, at thtat there Bar, set that there boy of mine, brought up and growed up to be a man, wot will errand you, message you, general-light-job you, till your heels is where you head is, if such should be your wishes. If it wos so, which I still don't say it is...let that there boy keep his father's place, and take care of his mother; don't blow upon that boy's father--do not do it, sir--and let that father go into the line of the reg'lar diggin', and make amends for what he would hav un-dug--if it wos so--by diggin' of 'em in with a will, and with conwictions respectin' the futur' keepin' of 'em safe....
Clearly, Jerry is, although uneducated, a shrewd man, who can and does prove to be an asset to Mr. Lorry, as well as the Manette/Darnay family. And, in Chapter XIV of Book the Third, Jerry vows to reform and give up his gravedigging and persecution of his wife for "floppin',"
Respectin’ a future spear o’ life, miss,” returned Mr. Cruncher, “I hope so. Respectin’ any present use o’ this here blessed old head o’ mind, I think not. Would you do me the favour, miss, to take notice o’ two promises and wows wot it is my wishes fur to record in this here crisis?”
Thus, Jerry becomes a reformed man, resurrected from his own sins. His character is an important part of the structure of A Tale of Two Cities as it provides contrast for the themes of resurrection and quiet and peacful domesticity; in addition, it also provides delightful comic relief.