The most important thing in the investigation of hwadu is to be awake to the hwadu continuously. Falling into the neutrality of no thought (mugi) at all and all the phenomena, ideas or malfunctions that arise in the process of taking up hwadu are functions of the production of the mind when one cannot be powerfully aware of the hwadu. The most desirable state for investigating the hwadu is the alert tranquility (seongseong jeokjeok) with respect of the hwadu.
When one investigates hwadu, the development of the state in which one has lost both sides, and the various frustrations and delusions do not rise or cease, is called “tranquility” (jeokjeok). This is a state in which the mind is calm and pure, just like a clean mirror or a clear lake in which there are no waves. Even in this state, the continuance of a feeling of doubt about the hwadu with a lively spirit that does not carelessly fall into neutrality is called “alert” (seongseong). It means to be clearly aware of the hwadu. It is just like the powerful shining of a bright light in a mirror.
Alertness is given priority out of alertness and tranquility in the investigation of hwadu. If one is not alertly aware of the hwadu, one will fall into dullness or neutrality or the realm of the demons. If one is completely aware of the hwadu, one will be immersed in the hwadu-samadhi and naturally open up the tranquil state.
Seon Master Bojo Jinul borrowed the words of Seon Master Yongjia Xuanjue (665-713) and said as follows:
And so Seon Master Yongjia said, “Although alert tranquility is correct, alert false thoughts are mistaken, and although tranquil alertness is correct, tranquil neutrality is wrong.” I do not agree to being blank in the midst of calm, so how can one produce the false mind by not giving rise to confused thought midst clarity? (Jinsim jikseol)
One must be “tranquilly alert” and must not be “tranquilly neutral.” This is to warn against the state of being merely tranquil without any thought. Therefore, in this process of taking up the hwadu, if one cannot clearly take up the hwadu, merely by being calm and tranquil, as soon as one falls into neutrality in the least it will be difficult to develop study.