A dharma teaching by Eihei Dogen (1200-1255), at the beginning of a summer retreat:
Once when Zikong was at Tiantong monastery in Siming at the beginning of a summer retreat he said, “For people in meditation the most important thing is that the nostrils be right; then the eyes must be thoroughly clear.
Then it’s important to realize the source and understand the explanation, and after that capability and its actualization are equally realized – only then can you enter among enlightened ones and demons as well, where oneself and others succeed together at once.”
What does this mean?
When the nostrils are right, everything is right. It is like a man in a house; if the master is upright, his family naturally influenced. But how can you get your nostrils straight?
An ancient sage said: “Certainty does not drift into a second thought; only therein you can enter the gate to our school.”
(from the Record of Sayings of Zen Master Dogen of Eihei;
source: Clearly, Thomas: Timeless spring; A Soto Zen Anthology. New York 1980, p. 100)