Even though David Copperfield focuses on, well, David Copperfield, it also provides a broad cross-section of mid-nineteenth century English life. David's adventures take him through many segments of society: from a rural village in Suffolk to coastal Yarmouth, from abusive country schools to degrading city factories, and from poverty and obscurity to fame and fortune. Given the wide range of this novel, it makes sense that the final chapter would go beyond just David to survey many of the different people we've met during its course.
The final chapter, "A Last Retrospect" (by the way, a retrospect is a look back over past events), is a lot like the other retrospects we've had in Chapters 18, 43, and 53. These chapters all take place in present tense, as though David is looking at them unfolding right before his eyes. This present tense contrasts with David's usual past-tense mode of narration. By changing up the mode of storytelling from past to present tense, Dickens is ratcheting up the emotional content of each of these chapters: they no longer take place in David's distant memories. Suddenly, the events narrated seem to be happening right up close.
Dickens uses this emotional storytelling tool six times to emphasize both extreme joy and extreme sorrow in David's life. These chapters work like punctuation – the exclamation points of the novel, if you will. And of course, the final chapter is the last exclamation point the book needs.
In Chapter 64, we find out that David and Agnes have been happily married and have many children. Miss Betsey is now 80 years old, still tough as nails, with Peggotty as her nurse. Peggotty continues to carry the old book David used to read to her to show to David's children. Now, David's sons fly kites with Mr. Dick. Mrs. Steerforth has gone senile and is nursed by the spiteful Miss Dartle. Julia Mills, the girl who brought David to Dora so many years before, has gotten spoiled and greedy with too much money. As an antidote to her bad temper, David offers us Doctor Strong, who keeps on working at his dictionary and living happily with Annie. Tommy Straddles has become wealthy and respected, and his household is filled with love. All of our loose ends have effectively been tied off, and the good, deserving people who started so tragically – David, Tommy Traddles, and even Doctor Strong – have lived and flourished happily. Like any good coming-of-age story, David has gone from lowly, troubled childhood to completely successful adulthood – and it's only taken him around nine hundred pages to get there.