Much has already been written on koans, yet there remains misunderstanding and confusion as to what koans actually are. In essence, koans are a form of spiritual practice unique to Zen. Since the days of the great Zen masters of ancient China, they have been used to help Zen students realize, refine, and embody the Buddha's teachings. Literally they are often baffling verbal expressions, puzzling or frustrating to logic, built around or taken from the sayings and doings of the ancient Zen masters, or occasionally from mythic/historical events in the life of the Buddha. Several books of koans, collections put together during the great T'ang era, are in regular use in Zen training centers today, the two most central being the Mumonkan, or Gateless Barrier, and the Hekiganroku, or Blue Cliff (sometimes translated as Blue Rock) Record.
Koans are not intellectual puzzles or conundrums, nor are they tricky and clever; rather, they are direct and profound. Every koan points to our True Face and True Home. To realize the essence of a koan is to realize the primal condition of one's own mind—a state of awareness, freedom, wisdom, and compassion. Viewed from this innate condition of Being, a koan is the clearest formulation of an essential truth—the truth of one's own nature. In essence, koans are tools designed by the spiritual geniuses of ancient China to help us realize the truth of our own nature and the nature of all living things, and to do so in the midst of our ordinary lives.
Working on koans under the guidance of an awakened and disciplined teacher is a concrete way of bringing to life the four bodhisattva vows chanted daily in all Zen centers, zendos, and monasteries:
All beings without number I vow to liberate.
Endless blind passions I vow to uproot.
Dharma gates beyond measure I vow to penetrate.
The great way of Buddha I vow to attain.
It is a tried and true way to awaken one's own sleeping buddha heart and mind and to liberate them to work for the welfare of others. The heart of Zen is not a mechanical pump. It is a roaring lion, and it is radiant.
Not everyone practicing Zen necessarily finds koan training to be his or her best mode of practice. Some people work on koans for a while and then choose to work on one fundamental question or do shikantaza, the practice of pure attention. Most practitioners start with breath-counting or following the breath and begin koan training or shikantaza later. There is no set path. Still, as koans reveal so much of Zen tradition and its uniquely creative style, dynamic spirit, and profound wisdom, commentaries on them can benefit anyone with a genuine interest in spiritual practice.
Actually everything, just as it is, is a koan, the expression of perfection. To realize this perfection is the working out of a living koan. All koans—and there are many of them—express this perfection in different forms, but all of them reveal the essential perfection of existence lying beyond the realm of ever-changing appearances. Every koan points to our Original Mind and is designed to bring us to the realization of it. You could say that all koans have a fundamental purpose—to lead us to our own real home, the one we knew before our parents gave birth to us.