Sweep away all dharmas.
Separate from all marks.

Those who do not understand the method of Chan investigation may treat it like chanting the Buddha’s name, thinking that the more you chant the better it is. That would be a mistake. Inquiry into the meditation topic is not done by chanting it. The best way is to stretch the resonance of the inquiry so that it lasts for a few hours without ending. That inquiry could even continue for eighty-thousand great kalpas without interruption. That would truly be investigating Chan. Why do we investigate “Who is mindful of the Buddha?” The word “who” is basically superfluous, but we are like monkeys, always looking around for something to do. With the word “who” acting as a shield can deflect all those idle thoughts.

This Dharma-door uses poison to fight poison. Only when we are free of all random thoughts can we be said to be diligently wiping the mirror of our mind clean at all times. To investigate Chan simply means to diligently wipe the mirror of the mind clean. Why must we keep wiping it clean? We must do that to keep the mind from attracting dust. This is the Dharma-door of “sweeping away all dharmas, and separating from all marks.”

If you do not use Dharma-selecting vision so that you recognize true Dharma, then you do not really know how to investigate. If you do not learn how to investigate, your efforts will just be wasted. That is because if you fail to recognize proper Dharma, you may well end up following
deviant dharmas. That is why Dharma-selecting vision is so important.