The patriarch said, "Think neither good nor evil. At this very moment, what is the original self of the monk Myo?" At these words, Myo was directly illuminated. His whole body was covered in sweat. He wept and bowed, saying, "Besides the secret words and the secret meaning you have just now revealed to me, is there anything else, deeper still?"
The patriarch said, "What I have told you is no secret at all. When you look into your own true self, whatever is deeper is found right there." Myo said, "I was with the monks under Obai for many years but could not realize my true self. But now, receiving your instruction, I know it like a man drinking water and knowing whether it is cold or warm. My lay brother, you are now my teacher."
The patriarch said, "If you say so, but let us both call Obai our teacher. Be mindful to treasure and hold fast to what you have attained."
I sense several concepts in this koan, running from how to attain buddhahood to how to retain it to what you are supposed to do with it.
Myo is offered the robe, but Eno's words have a double meaning. The robe is only a symbol, so fighting over it is foolish. That's the reason it should not be fought over. Myo can't pick up the robe anymore than he pick up the insight he seeks. Nor can either be given to him. This reminded me of a passage from Bodhidharma's Bloodstream Sermon:
"Trying to find a buddha or enlightenment is like trying to grab space. Space has a name but no form. It's not something you can pick up or put down. And you certainly can't grab it." (source: The Zen Teaching of Bodhidharma, translator: Red Pine)
Myo cannot pick up what he is seeking, but he is illuminated when Eno advises him to look within ("at this moment, what is the original self of the monk Myo?"). Thus, Myo attains enlightenment. Neither the robe nor instruction, if given, leads to enlightenment. This comes from within.
Eno fends off Myo's question about "anything else, deeper still" by again urging him to look to himself ("your own true self"). This is done independent of good or evil...or any sort of mental assessment of what true self means or represents. It just is.
Lastly, Eno urges Myo to "hold fast to what he has attained." Without doing this, a moment of enlightenment is just that: a moment. A brief flash of illumination and then darkness again. Enlightenment must be retained and inform us from then on if it is to have any real value. Knowing is one thing; retaining and making use of what you know is something else.