The seven-day retreat, or “Ch’an seven, ” is a practice in which disciples gather for a period of intense meditation under the guidance of a Ch’an master. The attitude of disciples during this period is one of total dedication to the task at hand ─ to shed, at least for a period of time, all the vexations of mind and body, and to bring the mind to a state of supreme clarity.
Since Sakyamuni Buddha, there has been a tradition of setting aside a definite period for deep practice. The aim was to achieve realization within that period. We learn from the Buddhist sutras that there were various periods, ranging from seven days to fourteen, twenty-one, or forty-nine days, always a multiple of seven days. In some cases this period lasted as long as three months. Of course it was only when Buddhism entered China that the term “Ch’an retreat” developed. (The Chinese word ch’an is derived from the Sanskrit dhyana, and the Japanese zen in turn, from ch’an.) In fact, what we call a Ch’an retreat literally means “Ch’an seven.” In the Pure Land sect, the practice of reciting the Buddha’s name for seven days is called “Buddha seven.” Reciting Kuan Yin’s name for seven days was “Kuan Yin seven.” Some people practice repentance ─ prostration for seven days, and that would be “repentance seven.” These are periods when one practices with more dedication and energy than usual, with the goal of achieving significant results.
Why seven days or a multiple of seven days? Our mental states are influenced by our physical states, which in turn are influenced by the cosmos. Nature itself seems to take seven days as a definite period. This concept of seven days is very ancient. It may come from the observation of celestial bodies. In the Bible, God created the world in seven days. In India the seven days were related to the seven planets. In ancient China this period was called “one come-and-go.”
Our body is a small universe, a microcosm, and it tends to reflect the great universe, the macrocosm. Our body and mind seem to demonstrate a cycle of seven days. Thus we take seven days as the optimum period of practice. So we can go on the first seven days, the second seven days, and the third seven days to help us to get onto a smooth and diligent path of practice. In Japan it is called sesshin, meaning “uniting or transmitting, the mind.” This can be interpreted on one hand, as the roshi, or teacher, taking away the student’s vexed mind and enabling him to achieve enlightenment. On the other hand, the student takes the mind from the roshi.
— Getting The Buddha Mind by Master Sheng-Yen (page 11-12)