Sometimes it might be useful to step outside of the stream of time and meet the minds of the wise who died long ago. The Zen ancestors had stumbled on a method to change the heart, and the problem they had was to pass on what they had discovered. There wasn't an obvious way to do this, so they invented koans. The idea is that when you spend time with a koan, it will give back the radiance in the heart of the one who made it. Koans might be imagined as vials of ancient light.
— John Tarrant, Bring Me the Rhinoceros