The basic teaching of Buddhism is the teaching of transiency or change. That everything changes is the basic truth for each existence. No one can deny this truth and all teaching of Buddhism is condensed within it. This is the teaching for all of us. Wherever we go this teaching is true. This teaching is also understood as the teaching of selflessness. Because each existence is in constant change, there is no abiding self.

Part 4, No. 1. "Transiency" - Zen Mind, Beginner's Mind (1973)