Zazen is a kind of yoga, a joining of body and mind in which the entirety of body and mind is engaged. Body and mind are “not two”; that is why we can call them “bodymind.” That being said, there is a physical component to zazen. We sit as best we can in a balanced, stable, and still posture which nurtures a balanced, stable, and still state of mind, the mental component of zazen. ... We are able to drop away all thoughts of the body in that posture, much as a runner drops the body in her running or a dancer in his dancing. They become so at one with the body and the action that the body is dropped from awareness. This is zazen of the body.
In the mental component to zazen we do not grab onto thoughts, do not engage in judgments, and sit in the wholeness and completeness of zazen itself. We experience “goallessness” and the realization of “nothing more to attain, no other place to go.” This is zazen of the mind.
However, there is also zazen in which both body and mind (or bodymind) are dropped away. The mind is spacious, the body is stable
and balanced. The hard borders between the self and the rest of life soften and sometimes fully drop away. To realize this state is “the accordance of the practice and realization of the Buddhas and Ancestors.” In other words, the doing of zazen is the realization of zazen.
The sentence “There is sitting of the body and mind dropped away, which is not the same as sitting of the body and mind dropped away” is a bit confusing. According to Nishijima Roshi and others, it may mean that the mere intellectual idea of this dropping is not the same as the actual doing and experiencing of dropping.