Zen is a development of Mahayana Buddhism, the Greater Vehicle, the Pure Land Buddhism.
What differentiates the Zen tradition from other traditions of Mahayana Buddhism is the legend of Bodidharma; who "for nine years remained seated in meditation before the wall of a monastery until his legs withered away."[i] While in the posture of za-zen, the sitting meditation, Bodidharma attained enlightenment.
The sitting and breathing meditation is done in order to balance the physical center of the practitioner. The goal is to set the body at perfect ease so that the mind may escape from it.
Having attained enlightenment through the sitting meditation Bodidharma became the first Patriarch of Zen. Bodidharma transmitted the "Buddha mind" to his disciple Hui-ko, who became the second Patriarch of the Zen tradition.
The technique of Za-zen is structured accordingly
The main point for the sitter is to have his ears and his shoulders, nose and naval stand to each other in one vertical plane, while his tongue rests against his upper palate and his lips and teeth are firmly closed. Let his eyes be slightly opened in order to avoid falling asleep.[ii]
The Zen tradition claims that this posture is particularly useful for acquiring the meditative state of mind. Though this "special posture is recommended...Zen has nothing to do with the form the body may take."[iii]
The sitting and breathing meditation is the heart of Zen, but the Zen mind is not bound by it.
The sitting and breathing meditation, za-zen is supposed to lever the mind into Buddha consciousness. It is in the meditative state that the Zen practitioner attempts to plumb the meaning of the sutras or koans, nevertheless, the Zen Masters maintain that:
The experience of enlightenment is not dependent on meditation; there is no causal connection between the two. Meditational practice is not the cause nor the condition for coming to a realization. Once awakened to wisdom, the mind sees nature, its own nature, which is identical to Buddha nature.[iv]
Meditation upon the sutras is the time honored tradition of Buddhism, and as such Zen Buddhism has a high regard for the sutras. The sutras are considered to be the writings of those who spoke with true Buddha consciousness. Reading "the sutras continued to be held in high regard [but] it was more in meditation than in study that efforts were made to appropriate the sutras."[v]
In Zen there is both a deep reverence for, and a complete willingness to depart from all norms, and traditional forms.
The Zen Master holds this view of the sutras and their most revered mediation practices, because of the prevailing belief that any strict or formalized adherence to specific practices, rituals, or methods can serve to obstruct the individual from the attainment of enlightenment.