One of the central themes in this novel is that of marriage and what a good marriage looks like. The novel presents the reader with various examples, but interestingly, it is important to note that Dr. Strong and Annie act as a kind of example of a good marriage. After Mr. Dick manages to bring them together again to foil the schemes of the evil Uriah Heep in trying to separate them, Annie makes the following comment that could be regarded as the central motto of the story:
There can be no disparity of marriage like unsuitability of mind and purpose.
These words strike David to the very core of his being, as he realises that his marriage to Dora is not based on equality of mind and purpose because they are completely different characters who will never be able to be reconciled to each other. Dickens is thus arguing that true marriage can rest on equality of mind and purpose alone, and that these factors are more important than age or class or other differences, as is shown by the massive age gap between Annie and Doctor Strong. Of course, once Dora is fortunately killed off by Dickens, David is free to enjoy the kind of marriage he dreams about with Agnes.
One of the themes of David Copperfield is the way in which the poor suffer but conduct themselves with great honesty and nobility. For example, Ham lives in a house made out of a boat and has little money, but he is an honorable man who lives neatly and respectfully. David Copperfield describes Ham's simple house as "the perfect abode" because it is so tidy and welcoming. Mr. Peggotty, Ham's uncle, is (according to Peggotty, David's housekeeper) incredibly generous. She describes Mr. Peggotty, her brother, in the following way:
"The only subject, she informed me, on which he ever showed a violent temper or swore an oath, was this generosity of his; and if it were ever referred to, by any one of them, he struck the table a heavy blow with his right hand."
Mr. Peggotty is poor but generous; he is also so humble that he hates for others to even refer to his generosity.
The poor in the novel are generally far more virtuous than the rich; for example, the rich James Steerforth, while once a good friend to David Copperfield, seduces the innocent Emily and then tries to convince her to marry one of his servants. It is generally among the poor that David finds virtue in this novel, even though the poor suffer. David himself suffers a great deal from poverty before his great aunt helps him, and Dickens suggests that the suffering of the poor makes them nobler than the rich.