Here is a short passage from Keizan's Record of the Transmission of Illumination (Denkoroku), Chapter 9. I stumbled on it again last night and it struck me as a wonderful summary of the path. This is from Bodiford's translation (modified, of course):
"The followers of the ancestral teachers proceed by 'not relying on scriptures,' 'pointing directly,' 'individually transmitting,' and by 'seeing nature and attaining buddhahood.'
"Thus, in order to let people know about the matter of 'pointing directly,' there is no method other than inducing them through individual transmission.
"One can only proceed by utterly cutting off the faculty of mind, such that white scum forms at the edges of the mouth. This does not mean that words are to be shunned or that silence is to be commended. It is simply to let you know that your mind is 'such.'
"It is like pure water, like empty space. Making it pure and clear, this is 'interpenetration without obstruction.'”