The Imagination
Many of Lamb's essays revolve around imaginative conceits, and the world that Lamb describes is most easily understood through his wild imagination. This plays out in novel fantasies such as the days of the month partying together and a boy eating a pig burnt by a house fire, as well as in the fabrications of something similar to Lamb's own life, such as the made up workers in the South Sea House or his fictive children in "Dream-Children; A Reverie." The innovation that Lamb brought to the essay was this very sense of the imagination, helping expand the form from its philosophical roots.
Class Vs. Class
Lamb is very interested in the distinction between social class and the type of class one exhibits (i.e. how a man comports himself). A trope in these essays is the idea that the rich don't really have any class, that they simply indulge their whims but live life rather insincerely. On the other hand, Lamb often depicts the poor and marginalized as noble people who struggle to enjoy themselves within their modest existence. Look no further than "The Praise of Chimney-Sweepers" to find the type of person Lamb considers noble. A debate on the merits of privilege is central to the essay "Old China."
Mischief
Lamb himself is a bit of a mischievous writer. For example, he draws his reader into a heart-wrenching story that ends up being little more than a dream, or crafts an elaborate ruse like the one in "The South-Sea House." But we also see him valuing the mischievous, whether that's April Fool's Day in "Rejoicings Upon the New Year's Coming of Age," or Bo-bo in "A Dissertation Upon Roast Pig." Lamb's playful sense shines through all of these essays, as his objective is to keep his reader entertained, just as he himself liked to be (if "Ellistoniana" is any clue).
Skepticism in Religion
A complicated relationship with religion is developed throughout the course of these essays. Lamb clearly has a spiritual side and his own understandings of living life in accord with God, but he frequently takes organized religion and people hypocritically wielding religion to task. A prime example of his ambivalent attitude toward religion comes with "Grace Before Meat," when he laments both the rich people who recite a rote, meaningless grace before yet another sumptuous banquet as well as people who flippantly make a joke about saying grace. What's clear about Lamb is that he has a clear sense of ethics and a strong moral compass, yet disagrees with the way that religion guides other people's ethics and morality.
Kinship
We know from Lamb's biography that he was particularly close to his sister Mary, and we can glean from these essays that he gave primacy to his family relationships. Whether it's the conversation with Cousin Bridget in "Old China" or the tales told in "Dream-Children; A Reverie," Lamb likes to demonstrate the influence of the people close to him. Yet that sense of kinship is not limited to his family. Rather, it's an attitude that extends to many of the subjects of his essays, be it friends like Elliston and James White, his beloved hero John Milton, or the chimney sweeper who laughs at him for slipping on ice. While Lamb is a proponent of solitary reading, he is constantly advocating for a life lived with others.
Storytelling
While essays are non-fiction, Lamb uses the theme of storytelling to push the boundaries of the form, often dabbling in fiction. For instance, his stories of the tea ceremony depicted on a piece of China and the various pork-related stories in "A Dissertation Upon Roast Pig" serve to conjure fictional histories. There are also the stories he tells of the people he loves, or the stories he relays from friends. In all of these, Lamb expands the typical boundaries of the essay form, creating rich, human, and consummately living prose.
Memory and Nostalgia
Lamb is nothing if not a nostalgist, and so many of his essays are rooted in recalling something from the past. Sometimes this is painful stuff, such as his rejection by his unrequited love Alice. But in the chimney sweepers, Lamb sees something of himself as a boy, and in the story about James White throwing them a banquet, he's fondly remembering both a person and and event that are history. He loves old china specifically because it bears some marks of a past, showing that Lamb's nostalgia is not for a specific time or state of affairs, but more broadly a yearning and affection for past times.
