As someone who had spent his life exploring the hidden interconnectivity of disparate emblems and ideologies, Langdon viewed the world as a web of profoundly intertwined histories and events. The connections may be invisible, he often preached to his symbology classes at Harvard, but they are always there, buried just beneath the surface.
With this statement, Langdon describes a major theme of the novel—the idea that secrets lie all around us awaiting interpretation. From the beginning of the novel, when Saunière leaves a mass of secrets and puzzles around his body, explicit examples of puzzles and codes abound. Some of the puzzles and codes are known to Langdon already, through his studies, and some are not.
Other connections that are buried just beneath the surface are the pieces of knowledge that the characters need in order to solve the mysteries. These pieces of knowledge are already known to the characters, but they must remember them and fit them together in the right way. Langdon is continually experiencing revelations. For example, he suddenly remembers that the Knights Templar worshipped a “head stone” of a god named Baphomet. Another time, he realizes that Saunière was referring to the apple when he named the orb that should have been on Newton’s tomb. Sophie is also in the habit of suddenly remembering important information. At the end of the novel, she recalls that she saw her grandfather talking to her grandmother when she was younger and they were visiting Rosslyn Chapel. According to Brown, Sophie remembered this all along and just needed the right impetus to uncover it.