It is now several years since I noticed how from the time of my early youth I had accepted many false claims as true, how everything I had later constructed on top of those falsehoods was doubtful, and thus how at some point in my life I needed to tear everything down completely and begin again from the most basic foundations, if I wished to establish something firm and lasting in the sciences.
-- The Narrator (First Meditation paragraph 1)

Importance: In the first line of the book, Descartes introduces the central project of the Meditations. It gives both the motivation for the project, by showing how a few falsehoods can infect all our knowledge. It also shows the vast scope: the purpose of the meditations is to "tear everything down completely." As such, the quote hints at the extreme lengths Descartes will go to in order to make his new foundations of knowledge secure from doubt. The...