Obviously, the biggest symbol in this novel is the House of the Seven Gables itself. Hawthorne helps us out with this one by putting it right there in the title! The house represents a ton of things: first, it stands in for the Pyncheon family as a whole. The reason Colonel Pyncheon accuses Matthew Maule of witchcraft is so that he can build a large, fine house as a legacy to his family. But Colonel Pyncheon also curses both house and family by building the house on the foundations of Maule's hut. How can the Pyncheon family flourish when it's literally rooted in the legacy of a murdered man?
The house's condition also tells us something about the state of the Pyncheon family through the years. When Colonel Pyncheon builds the house, it's luxurious and constructed according to the latest fashion. Even in the time of Mr. Holgrave's tale, the house has "that pleasant aspect of life which is like the cheery expression of comfortable activity in the human countenance" (13.12). In other words, the house looks lively and is bustling with a large family. In the time of the novel's present, in the 1850s, the House of the Seven Gables has grown ancient and dark. Similarly, the family has dwindled to a few scattered, warring members – Hepzibah, Clifford, Jaffrey, and Phoebe Pyncheon. The aging of the house reflects the aging (and diminishing) of the Pyncheon family itself.
The house's weathered, gloomy appearance also marks it as a symbol of past times. The portrait of Colonel Pyncheon reminds its inhabitants every day of the origins of the Pyncheon family. The house is filled with artifacts of days gone by: Colonel Pyncheon's chair, Alice Pyncheon's harpsichord, even the old shopkeeper's locked shop door. These relics accompany the literal ghosts of Pyncheons past. The shopkeeper of a hundred years earlier is supposed to float anxiously through his abandoned shop, and Alice Pyncheon can occasionally be heard playing her harpsichord. The night of Judge Pyncheon's death brings out a full procession of deceased Pyncheons. This house is both literally and metaphorically haunted by the past. Hepzibah and Clifford Pyncheon both respond to the House of the Seven Gables as a physical manifestation of their family's tortured past – not a very peaceful relationship to have with the place where you live.
Last but not least, the house's grim appearance sets the gloomy tone and Gothic genre for the whole novel. Its dark passageways and dim rooms give it a sense of unease. The lack of light seems only appropriate for a house as haunted as this one.