The section in Shobogenzo, Genjokoan about how awakening to the truth that "the many things actualize awareness of the self" is the function of Zen practice (indicating that our true nature is the true nature of the universe). The text goes on to indicate the nature and function of enlightenment and delusion. Genjokoan states:
Those who are enlightened about delusion are buddhas.
So being "enlightened about delusion" means awakening to the reality of delusion. That is, realizing what delusion truly is. This could be likened to being shown the cause of a magician’s illusions: mirrors, wires, hidden compartments, etc., thus being able to grasp the reality of the illusion. The reality of the illusion (the mirrors, wires, hidden compartments) is existent, and the illusion is a real characteristic of its existence. Similarly, when realizing the cause of delusion: misperception or partial perception, of true nature, we realize the reality of delusion. The reality of delusion (misperception or partial perception of our own true nature) is existent, and delusion is a real characteristic of its existence. Those who are "enlightened about" this are called "buddhas."
Next, the Genjokoan says:
Those who are deluded about enlightenment are ordinary beings.
To be "deluded about enlightenment" is to view enlightenment as being something outside or apart from ourselves or the everyday world. Those who are aware of their true nature are called buddhas; those who are unaware of their true nature are called ordinary beings. Flowers fall, weeds flourish; cocks crow, dogs bark. The Genjokoan goes on:
There are people who continue to realize enlightenment based on enlightenment.
Dogen’s emphasis on post-kensho practice and enlightenment is rarely matched in Zen literature. In many places throughout his works he insists that the initial experience of enlightenment is just the beginning of genuine practice-enlightenment. Of course, enlightenment for Dogen is only authentic as practice and enlightenment. In his works, he often refers to realizing enlightenment based upon enlightenment (often using the Zen ancestors of the past as examples of how to approach the lifetime process of deepening and refining our realization). The Genjokoan continues:
There are people in the midst of delusion adding to delusion.
Dogen does not seem here to be simply repeating himself, but to be indicating something else. In Shobogenzo, Keisei-Sanshiki, Dogen uses the same phrase (as best as I can tell) in a manner that suggests a deeper implication:
When [a person] tells people who do not know the will to the truth about the will to the truth, the good advice offends their ears, and so they do not reflect upon themselves, but [only] bear resentment towards the other person. As a general rule concerning actions and vows, which are the bodhi-mind, we should not intend to let worldly people know whether or not we have established the bodhi-mind or whether or not we are practicing the truth; we should endeavor to be unknown. How much less could we boast about ourselves? Because people today rarely seek what is real, when the praises of others are available, they seem to want someone to say that their practice and understanding have become harmonized, even though there is no practice in their body, and no realization in their mind. "In delusion adding to delusion" describes exactly this.
Gudo Nishijima & Mike Cross, Master Dogen’s Shobogenzo, Keisei-Sanshiki, Book 1, p. 91 (italics added)
In this passage, Dogen seems to define the condition of "increasing delusion in the midst of delusion" as the denial of delusion. That is to say, when people in delusion deny they are deluded (or assert they are enlightened) they are "in delusion adding to delusion." Looking at Case One of the Blue Cliff Record may shed some light on this particular condition. The koan reads:
Emperor Wu asked Bodhidharma, "What is the ultimate meaning of the holy truths?"
Bodhidharma said, "Vast emptiness, nothing holy."
The Emperor asked, "Who is facing me?"
Bodhidharma responded, "I don’t know."
The Emperor did not understand. After this Bodhidharma crossed the Yangtse River and traveled to the kingdom of Wei.
Later the Emperor asked Master Chih about it.
Master Chih asked, "Do you know who this man is?"
The Emperor said, "I don’t know."
Master Chih said, "He is the great bodhisattva, Avalokitesvara, transmitting the confirmation of the buddha-mind."
The Emperor was regretful and wanted to send an envoy to bring Bodhidharma back.
Master Chih said, "Don’t say you will send someone to bring him back. Even if everyone in China went after him, he would not return."
Commenting on the line "The Emperor did not understand," Engo (Yuanwu - the editor of the Blue Cliff Record) says, "Too bad! Still, he’s gotten somewhere." (Cleary & Cleary) Might the meaning of Engo’s comment, "Still, he’s gotten somewhere," illumine what Dogen means by "in delusion adding to delusion"? In following the reasoning here, Emperor Wu could be understood as "adding to delusion" when he thought he knew something (or asserted his enlightenment). However, (although he is still in delusion) after his meeting with Bodhidharma, he admits that he does "not understand," that is, he does not deny his own delusion. The Emperor is in delusion (i.e. not enlightened), but he is no longer adding to delusion (by asserting his enlightenment).
Clearly, recognizing and acknowledging the reality of our own delusion is a prerequisite to enlightenment. For how or why would one aspire to, or arouse the will for enlightenment if they failed to recognize and acknowledge their own delusion? Hence, Dogen’s words, "Those who are enlightened about delusion are buddhas" could be read as meaning that the recognition and acknowledgement of delusion is simultaneous with enlightenment. Throughout the Shobogenzo, Dogen continuously asserts the nondual nature of delusion and enlightenment; but he never says (to the best of my knowledge) that buddhas are free from delusion, as is often implied by much of the contemporary literature of Zen. Indeed, as Genjokoan goes on to say:
When buddhas are buddhas, they do not know they are buddhas.
This line reminds us that when buddhas are experiencing the condition of Buddhahood, there is nothing but Buddha in the whole universe. This condition is sometimes described in Buddhist literature as the state where the known and the knower (or actor and action) are one. Obviously, for a buddha to have the thought, "I am a buddha," they would have to perceive themselves as something (buddha) in opposition to something else (not buddha), hence; they would not be in the condition of Buddhahood. That does not mean there are no buddhas, as the Genjokoan points out next:
Nevertheless, buddhas are buddhas and continuously actualize Buddhahood.
The condition of Buddhahood is not something that is gained, but something that is discovered and activated; that is, the nature of delusion is illumined and our original Buddhahood is realized. Of course, this experience is only called Buddhahood to differentiate it from delusion. When speaking of a state beyond delusion we call it "Buddhahood." However, in the absolute sense, as in Dogen’s opening lines to Genjokoan, there is nothing to be grasped (no buddhas, no ordinary beings, etc.) and in the transcendent sense, buddhas and ordinary beings always contain and include each other.
The classic Zen records tell us that in the actual experience of Buddhahood all names and labels are meaningless; for from the perspective of oneness or emptiness, differentiation does not exist. Even "oneness" is a relative term–that is, oneness is relative and only valid in contrast to multiplicity. Therefore, when differentiation is truly dissolved so, too, is Buddhahood. One wonderful Zen expression of this principle is a verse attributed to Ananda, one of Buddha’s disciples and the traditional Second Ancestor of Zen in India:
When we are awake to the truth, even the non-dharma does not exist.
The Transmission of the Lamp, Sohaku Ogata, p. 10