At the heart of the variety of Zen that Dōgen taught are a number of key concepts, which are emphasized repeatedly in his writings. All of these concepts, however, are closely interrelated to one another insofar as they are all directly connected to zazen, or sitting meditation, which Dōgen considered to be identical to Zen, as is pointed out clearly in the first sentence of the 1243 instruction manual "Zazen-gi" (坐禪儀; "Principles of Zazen"): "Studying Zen ... is zazen".[13] In referring to zazen, Dōgen is most often referring specifically to shikantaza, roughly translatable as "nothing but precisely sitting", which is a kind of sitting meditation in which the meditator sits "in a state of brightly alert attention that is free of thoughts, directed to no object, and attached to no particular content".[14]
[edit] Oneness of practice-enlightenment

The primary concept underlying Dōgen's Zen practice is "oneness of practice-enlightenment" (修證一如 shushō-ittō / shushō-ichinyo). In fact, this concept is considered so fundamental to Dōgen's variety of Zen—and, consequently, to the Sōtō school as a whole—that it formed the basis for the work Shushō-gi (修證儀), which was compiled in 1890 by Takiya Takushū (滝谷卓洲) of Eihei-ji and Azegami Baisen (畔上楳仙) of Sōji-ji as an introductory and prescriptive abstract of Dōgen's massive work, the Shōbōgenzō ("Treasury of the Eye of the True Dharma").

For Dōgen, the practice of zazen and the experience of enlightenment were one and the same. This point was succinctly stressed by Dōgen in the Fukan Zazengi, the first text that he composed upon his return to Japan from China: "To practice the Way singleheartedly is, in itself, enlightenment. There is no gap between practice and enlightenment or zazen and daily life".[15] Earlier in the same text, the basis of this identity is explained in more detail:
“ Zazen is not "step-by-step meditation". Rather it is simply the easy and pleasant practice of a Buddha, the realization of the Buddha's Wisdom. The Truth appears, there being no delusion. If you understand this, you are completely free, like a dragon that has obtained water or a tiger that reclines on a mountain. The supreme Law will then appear of itself, and you will be free of weariness and confusion.[16] ”

The "oneness of practice-enlightenment" was also a point stressed in the Bendōwa (弁道話 "A Talk on the Endeavor of the Path") of 1231:
“ Thinking that practice and enlightenment are not one is no more than a view that is outside the Way. In buddha-dharma [i.e. Buddhism], practice and enlightenment are one and the same. Because it is the practice of enlightenment, a beginner's wholehearted practice of the Way is exactly the totality of original enlightenment. For this reason, in conveying the essential attitude for practice, it is taught not to wait for enlightenment outside practice