In Chapter 3, David meets Peggotty's extended family. Peggotty uses two idioms to describe Mr. Peggotty:
[Mr. Peggotty] was but a poor man himself, said Peggotty, but as good as gold and as true as steel—those were her similes.
"Good as gold" and "true as steel" don't have immediately obvious meanings in the literal sense. "Good as gold" stems from the introduction of paper money in the two centuries prior to Dickens's novel. Many people were concerned about how the paper money could be valuable if it was simply writing on a piece of paper, and the phrase "good as gold" assuaged these concerns. It meant that if someone gave you a banknote worth 20 pounds of gold, it was the equivalent of being handed the 20 pounds of gold itself (and it was much more convenient for everyone involved). The phrase took on broader meaning as it was used more, and Peggotty uses it to describe Mr. Peggotty's good character. "True as steel," meanwhile, means he's trustworthy. Even though steel is an inanimate material that does not have human characteristics, it has long been a notoriously reliable building material. To be as true as steel is to be similarly dependable.
David is quick to point out that these idioms (which, as he writes, are also similes) come from Peggotty, not him. This insistence might indicate a hint of snobbery on David's part. Working class characters are generally the most likely to use idioms in the novel. David is keen to set himself apart not only from the working class but also from the likes of people who can't come up with their own original ways of describing people and things. After all, he prides himself on being a writer. Then again, he also prides himself on being a self-made writer and on having more sympathy for the working class than many others. By using Peggotty's idiomatic expressions, the narrator highlights his humble origins and his appreciation for the working class, even as he sets himself apart from them.
In Chapter 8, David goes home from Salem House for the holidays, and the Murdstones are absent for his first afternoon there. He uses imagery and a simile to describe how their return to the house shatters the nostalgic fantasy of life back with his mother and Peggotty:
It appeared to my childish fancy, as I ascended to the bedroom where I had been imprisoned, that they brought a cold blast of air into the house which blew away the old familiar feeling like a feather.
In a literal sense, the cold blast of air is simply an effect of the time of year. If someone opens the door during winter in England, cold air will come inside. The reason David remembers the cold air, however, is because of its metaphorical significance. It contrasts the warmth he felt in his mother’s arms when it was just her, Peggotty, and David’s new half-brother. Just as winter kills off a lot of life, the Murdstones bring with them the death of the lively atmosphere in the house.
Although the Murdstones hold a lot of power over David, his mother, and Peggotty, the simile comparing the "old familiar feeling" to a feather that is easily blown away indicates how fragile the feeling of warmth was to begin with. Even at his young age, David is already indulging in nostalgia when he spends this perfect afternoon with his mother, brother, and Peggotty. Their collective warmth and happiness is an attempt to reclaim something that was lost as soon as Clara Copperfield brought Mr. Murdstone into their lives. The cold blast of winter air is a cold blast of reality. The Murdstones and the cold air alike are reality knocking down the door of the little family’s warm fantasy. Even if the Murdstones had remained out, David would eventually have had to go to "the bedroom where I had been imprisoned" because the house has been indelibly transformed by the Murdstones' abuse.
In Chapter 32, David must grapple with the knowledge that his friend Steerforth has seduced Emily and betrayed the Peggotys. He uses a simile to describe how this news affects his relationship to Steerforth:
What his remembrances of me were, I have never known—they were light enough, perhaps, and easily dismissed—but mine of him were as the remembrances of a cherished friend, who was dead.
The idea that Steerforth is as good as dead to David on the one hand demonstrates how seriously David takes this transgression. He seems to intend never to speak to Steerforth again as a friend. Leading Emily astray is an unforgivable act. On the other hand, the idea that Steerforth is like a dear friend who is now dead also demonstrates how seriously David takes their friendship. The loss of Steerforth causes the same kind of pain that the loss of David's mother caused him. What's more, just as standing at his mother and brother's grave made David feel acutely what it was like to be held close as a young child, the loss allows the positive memories of Steerforth to stand out as formative, cherished moments.
David's mother was imperfect and often failed to protect him. Still, her dying seems to have preserved her in his memory as an overwhelmingly positive figure. Likewise, Steerforth's friendship becomes even more precious to David because of its loss. David seems able to divide people, including his mother and Steerforth, into their good parts and their bad parts. This ability is part of what makes David a suitable protagonist for a Bildungsroman. He is able to frame everything he experiences as a positive factor in his journey to self-actualization. Even after Steerforth's betrayal, David refuses to reevaluate his past experiences with this "dead" friend because these experiences helped shape him. David is thus not forgiving, exactly, but he is remarkably appreciative of the lessons he learns from everyone he encounters.
As a Bildungsroman, David Copperfield is about the growth and success of its main character within Victorian society. In Chapter 64, at the close of the novel, a simile leaves the reader with the sense that David's journey of personal development has also prepared him for spiritual success that transcends Victorian society:
O Agnes, O my soul, so may thy face be by me when I close my life indeed; so may I, when realities are melting from me like the shadows which I now dismiss, still find thee near me, pointing upward!
David imagines how at the end of his life, reality will fall away "like the shadows I now dismiss" in the dying candlelight. Still, Agnes will be there, "pointing upward." This simile suggests that at the end of his life, Agnes will direct him to heaven, and the life he has led will reveal itself to be a false "shadow" of his eternal life in heaven. For all his struggle to make it in Victorian society, he imagines that his life there won't mean much in the end.
The idea that his real life will become a "shadow" is remarkable. Married life with Agnes is the apotheosis of David's journey: he has achieved professional success, and now he gets to have a stable family with the woman who is best suited for him. This is more than any of his parents or parent figures ever achieved. Clara Copperfield tried to create a stable family unit but ended up marrying an abusive man who led to her early death. Peggotty and Barkis come close, but they never have their own children. Mr. Peggotty and the Micawbers must go to Australia in order to find anything like David's success. Mr. Wickfield spent his life mourning his late wife. Miss Betsey and Mr. Dick do well enough for themselves, but they have an unconventional arrangement without marriage or children of their own. David's situation at the end of the novel represents the Victorian ideal that almost no one replicates.
Still, the simile at the end of the novel makes clear that even this wildly successful life is, to David, merely a rehearsal for a more real existence beyond. This deeply religious idea was popular in Victorian England. This is also not the first time it has come up in the novel: at their funeral, David imagined that death was a new beginning for his mother and half-brother. This simile at the end of the novel confirms that while David has met essentially all of his earthly goals, his journey will not be entirely complete until he dies and arrives in heaven.