Although sitting is the foundation of zazen [i.e., seated meditation], it is not just any kind of sitting. Not only must the back be straight, the breathing properly regulated, and the mind concentrated beyond thought, but, according to Dogen Zenji, one must sit with a sense of dignity and grandeur, like a mountain or a giant pine, and with a feeling of gratitude toward the Buddha and [those who came after him], who made manifest the Dharma. And we must be grateful for our human body, through which we have the opportunity to experience the reality of the Dharma in all its profundity. This sense of dignity and gratitude, moreover, is not confined to sitting but must inform every activity, for insofar as each act issues from the Bodhi-mind, it has the inherent purity and dignity of Buddhahood. This innate dignity of a person is physiologically manifested in her erect back, since she alone of all creatures has this capacity to hold her spinal column vertical…

In the broad sense, zazen embraces more than just correct sitting. To enter fully into every action with total attention and clear awareness is no less zazen. The prescription for accomplishing this was given by the Buddha himself in an early sutra: “In what is seen there must be just the seen; in what is heard there must be just the heard; in what is sensed (as smell, taste, or touch) there must be just what is senses; in what is thought there must be just the thought.”

Roshi Philip Kapleau
from The Three Pillars of Zen