Dogen answers by first saying that, when Master Bodhidharma first brought his teachings to China, the Buddhist clergy there was so shocked at how he was sitting Zazen ... that they actually called him the founder of the "'Zazen' or 'Zen' Sect". That shows how much the clergy in China at the time had forgotten about, or were not practicing, "Zazen".
Anyway, says Dogen, Zazen is rather different from mere practices of "concentration" or "meditation" as those words are usually used in Buddhist philosophy ... (a subject we shall discuss tomorrow) ...
Q. [Someone] asks, "Among the three kinds of training [in the precepts, concentration and wisdom] there is training in [concentration], and among the six Paramitas [the Perfections of charity, keeping the precepts, patience, diligence, the practice of meditation and wisdom] there is [included meditation], both of which all bodhisattvas learn from the outset and all bodhisattvas practice, regardless of whether they are clever or stupid. The zazen [that you are discussing] now is surely one of these [and already included]. Why do you say that the Tathagata's [Buddha's] right Dharma is concentrated in this [one practice of zazen]?"
A. I say: The question arises because this right
Dharma-eye treasury, the supreme and great method, which is the one great matter
of the Tathagata has been called the "Zen Sect." Remember that this
title"Zen Sect" was established in
That this Buddha-Dharma is the legitimate intention of the one-to-one transmission has never been concealed through the ages. In the order on Vulture Peak in ancient times, when the Tathagata gave the Dharma to Venerable Mahakasyapa, transmitting the right Dharma-eye treasury and the fine mind of nirvana, the supreme and great method, only to him, the ceremony was witnessed directly by beings among the celestial throng which are present in the world above, so it must never be doubted. It is a universal rule that those celestial beings will guard and maintain the Buddha-Dharma eternally; their efforts have never faded. Just remember that this [transmission of zazen] is the whole truth [and complete path] of the Buddha's Dharma; nothing can be compared with it.
From: Bendowa - A Talk about Pursuing the Truth - Nishijima-Cross [with some amendments according to Uchiyama]