What is an important and significant metaphor used in The DaVinci Code?

The Da Vinci Code is considered controversial since many of the assertions made in the story challenge traditional interpretations of religious history; for this reason, it seems appropriate to suggest that the Bible itself is the most striking metaphor used in the novel. Robert Langdon, a Harvard professor specializing in religious symbols and icons, is well-versed in history, architecture, and religion and in the story reveals little-known details that paint an interwoven picture containing the works of Leonardo Da Vinci, the Knights Templar, the Holy Grail, the Christian Church. Langdon can most accurately be described as agnostic, since he neither subscribes to the Christian faith nor denies the existence of God, and he asserts that the contents of the Bible are a metaphor for the truth, rather than actual, literal true stories passed down for generations.
The idea of the Bible as a metaphor through which truth can be found, rather than true history interpreted literally, is a stark contrast to the teachings of the Christian Church, but in this book as well as in its sequels, Langdon promotes the idea that science and religion are not opposing ideas that cancel one another, but simply alternate methods of telling the same story. Although Langdon questions whether keeping the secrets of the Grail might be a prudent step in preserving the faith of people who subscribe to a literal interpretation of the Bible, he nonetheless believes that those with true faith in God will be able to maintain that faith even if the Bible itself is considered a metaphor for arriving at truth.