The novel's style is self-conscious: the narrator is always reminding the reader that he is telling the story of his own life, and that his perspective has shifted as he has gotten older and looked back on events. For instance, in Chapter 43, he describes becoming an author:
I have come out in another way. I have taken with fear and trembling to authorship. I wrote a little something, in secret, and sent it to a magazine, and it was published in the magazine. Since then, I have taken heart to write a good many trifling pieces. Now, I am regularly paid for them.
In this passage, the narrator inhabits the perspective of himself at the start of his success as a writer. When he writes that, "Now, I am regularly paid for them," he uses the present tense. However, "now" does not refer to the time at which he is writing David Copperfield. Rather, it refers to the present at this paused point in the narrative, when he is soon to marry Dora and still makes the majority of his income by working as a stenographer. The chapter is entitled "Another Retrospect," and it looks back over David's young adulthood from the perspective of his early-career self. The narrator uses the present perfect tense as he names the earliest stages of his career: "I have come out in another way," "I have taken with fear and trembling," and "I have taken heart" are all retrospective observations from the David of Chapter 43 of how far he has come at this point in his life. By playing with verb tense, the narrator not only describes his own growth during this period, but also captures a sense of the pride he remembers feeling at the time about that growth.
Dickens frequently plays with verb tense in this novel. He especially uses the present tense to convey the immediacy of whatever memory he is exploring. This stylistic choice can serve not only to paint a vivid picture for the reader of the memory itself, but also to convey the strangeness of memory. Often, at least for the narrator, a memory completely takes hold of his mind and replaces present reality. In the case of the passage above, he gets inside the mind of his former self to truly inhabit the feeling of his growing confidence rather than simply describing it from his much older perspective.
Although the novel is at times sentimental and at times witty and ironic, it always returns to these interjections from the narrator that make clear the novel's self-awareness as a work of art and a work of memory. As he states in the first chapter, these self-conscious moments suggest that the narrator is in some senses unqualified to determine whether or not he is the hero of his own story.