The full title of the novel, Oliver Twist, Or, the Parish Boy's Progress, is an allusion to John Bunyan's wildly popular Pilgrim's Progress (1678). Bunyan's text describes the trials its main character, the aptly-named Christian, undergoes on the way to the Celestial City. Christian's trials are an allegory for the spiritual trials all Christians must undergo on the way to heaven.
Bunyan's book sparked what is arguably one of the original best-seller franchises, inspiring an array of collectors' items that people kept in their houses. It was still extremely popular in the 19th century. Dickens's readers would have recognized Oliver Twist's full title as a sign that this novel would describe a series of trials through which Oliver, as a representative of "parish boys" more generally, would gradually ascend to some kind of salvation.
In the broadest sense, the novel does describe Oliver's ascent out of poverty through a series of trials. But the title also evokes popular parodies of Bunyan's allegory, such as William Hogarth's Rake's Progress, a series of paintings that depict the moral downfall of a man who moves to London and gets involved in gambling and sex work. In Dickens's novel, Oliver has just as much potential to be corrupted as he does to be saved when he goes to London. The dual allusion to Pilgrim's Progress and its parodies contributes to Dickens's critique of Victorian England's social and legal systems: in this world, a virtuous but poor child like Oliver is in a precarious position. He may rise or he may fall, and it is mostly up to chance.
The novel goes so far as to parody Bunyan's text, as well as other popular sentimental fiction that suggests that the world is an obstacle course of temptations to test good Christians' character. For instance, in Chapter 3, Oliver manages to escape apprenticeship to a man who seems very cruel, but his fate nonetheless remains out of his control:
The next morning the public were once more informed that Oliver Twist was again to let, and that five pounds would be paid to anybody who would take possession of him.
Oliver is buffeted around the world like a piece of junk no one wants: the parish does not even try to sell him but in fact offers to pay anyone who will take him. The future trials he will face are not divine tests of characters, like they are for Bunyan's Christian. Instead, they are the result of bad luck and discrimination by a world that doesn't see him as human. Whereas Christian and characters in sentimental novels can control their fate by acting in morally upstanding ways, Oliver can only beg magistrates and other powerful people to take mercy on him.
In Chapter 48, when Sikes attempts to escape after killing Nancy, an allusion to Shakespeare's Macbeth heightens the stakes of Sikes's situation:
Up and down the ladders, upon the roofs of buildings, over floors that quaked and trembled with his weight, to under the lee of falling bricks and stones,—in every part of that great fire was he; but he bore a charmed life, and had neither scratch nor bruise, nor weariness nor thought, till morning dawned again, and only smoke and blackened ruins remained.
In Shakespeare's play, Macbeth launches a murder spree in pursuit of power, in part because he has heard a prophecy that convinces him that he can't be killed by anyone who has been birthed by a woman. When Macduff pursues him to bring him to justice, Macbeth tells him, "I bear a charmed life, which must not yield / To one of woman born." Unfortunately for him, it turns out that Macduff was not "born" in the traditional way, but rather through a cesarean section, so Macduff is able to kill him after all. This allusion makes clear that Sikes's "charmed life" is merely prolonging his death, as it does for Macbeth. In other words, the end is coming for him.
By evoking Macbeth, the novel suggests that villains' obsession with power is a pursuit that will ultimately result in their demise, both physically and psychologically. Sikes not only dies for his crime, but he also evidences the same kind of paranoia over the blood he has spilled as Lady Macbeth famously exhibits when she can't seem to wash all the blood of murder off her hands. Like Macbeth, Sikes eventually dies for the murder he has committed. But his death is a self-inflicted accident that happens in the course of his flight from the people who are trying to hold him accountable. Like Lady Macbeth, Sikes dies at his own hand after losing his mind from guilt and paranoia. The reader is left understanding that Fagin, who manipulated Sikes into killing Nancy, is the real Macbeth character. He maintains his criminal fiefdom by recruiting others to commit crime and even murder on his behalf. Macbeth famously describes life as "a tale / Told by an idiot, full of sound and fury, / Signifying nothing." In the end, Sikes, Nancy, the Artful Dodger, and other criminals seem to lead lives that "signify nothing." Of Fagin's crew, only Oliver maintains the possibility of a meaningful life because he resists manipulation by Fagin.
