Students of the Buddhadharma must have the Dharma-selecting Eye so they can recognize right dharmas and wrong dharmas, black dharmas and white dharmas, good dharmas and bad dharmas. Be sure you never take right as wrong and wrong as right; or black as white, and white as black; or good as bad, and bad as good--that's all upside-down. If you want to recognize these dharmas, you must certainly have the Dharma-selecting Eye.
First of all, you cannot have the mark of self. If you have the mark of self, all kinds of obstacles will arise, and you will have no wisdom. Once there is a mark of self, selfish thoughts arise, followed by thoughts of benefiting the self and thoughts of seeking and greed. If you do not obtain what you seek and crave, contentious thoughts arise, and you will struggle with others to see who is stronger.
If you can have no mark of self, then what is the self? Who am I? Ponder and investigate: "Who is mindful of the Buddha?" The question "Who...?" isn't meant to be recited. It's of no use if you keep reciting it. You must investigate it. Investigation can be compared to drilling a hole. When you drill all the way through, you will thoroughly understand.
If for one moment you don't understand,
For one moment you must investigate.
If for every moment you don't understand,
For every moment you must investigate.
Investigating doesn't mean guessing. You guess, "Well, I'm mindful of the Buddha, you're mindful of the Buddha, and he's mindful of the Buddha, too? So who's mindful of the Buddha?" You can keep guessing, but you won't get the answer. Rather, you must search for the "who." The word "who" is the Vajra King Jeweled Sword, the sword of wisdom. You must use the wisdom sword to cut through all other idle thoughts, and then wisdom will spontaneously appear.
If you don't understand the Dharma-door of investigating Chan and you think the more you recite the better, just like reciting the Buddha's name, that's a mistake. You don't need to recite many times, but ideally you should stretch out the sound and keep it going for a few hours, or even for eighty-four thousand eons, without a break. Then you're really investigating Chan.
Why do we want to 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. If there is the word "who" acting as a shield, then all those idle thoughts will disappear. This Dharma-door uses poison to fight poison. To investigate Chan simply means to diligently wipe (the mirror of the mind) clean. Only when we are free of all random thoughts are we "diligently wiping it clean at all times." We want to wipe it clean so it won't get dusty. This is the Dharma-door of "sweeping away all dharmas, and separating from all marks."
If you don't have the Dharma-selecting Eye and you don't recognize the true Dharma, then you won't know how to investi-gate. If you don't know how to investigate, then you're just wasting your effort. If you don't recognize the proper Dharma, then you'll follow after deviant dharmas. That's why the Dharma-selecting Eye is so important.
A talk given on the evening of December 4, 1982
at the City of Ten Thousand Buddhas