Kigen (Joyo) Dogen lived from 1200 to 1253 AD. He was born into a family of the court nobility, and studied a form of Zen in Japan before studying Zen meditation in China under the roshi [Zen teacher] Ju-ching. His chief work is the Shobogenzo. Here are quite simple adages from Dogen's Fukanzazengi. In that treatise he tells that contemplating the mind source is the essential art of zazen (meditation sitting) by the eko hensho technique of "turning the light around and looking back".
Zen is rife in colourful metaphors. Sozan, an early master of the same sect of Zen as Dogen, says, for example: "There is something fundamental in oneself, when one turns the light around (shifts attention from sense experience to the essence of mind) one ejects form, sound, smell, flavor, touch, and phenomena, and attains tranquility." And Dogen says in an early treatise on zazen [Zen sitting], "You should stop the intellectual practice of pursuing words and learn the 'stepping back' of 'turning the light around and shining back'; [and finally] the 'original face' [real nature, mind essence, original Buddha-nature] will appear." [Shz 9]
The art of looking into the mind source instead of pursuing thoughts and external stimuli is called eko hensho. The contemplation during eko hensho is not conceptual. There are many pointers around it to be found in Zen lore, using terms such as "before the Buddha appears in the world," before a single thought arises," to orient the mind in the eko hensho technique. [Shz 21n]
To illustrate such disentanglement, this essential art of zazen, as Dogen calls it: As the Zen master Yakuzan was sitting, a monk asked, "What are you thinking of, so still and intent?"
Yakuzan answered, "I am thinking of that which is not thinking."
The monk said, "How can one think of that which is not thinking?"
Yakuzan said, "It isn't thought." [Shz 10]
Dogen used koans, or Zen conundrums, but did not stress koans as much as is done in the Rinsai Zen sect or school. He also said, "the prime essential is sitting meditation (zazen)." He frankly counsels students not to get involved with other things than the act of Zen sitting so that the Way opens up. So deep meditation first, according to "first things first", at any rate [Shz 14].
Stop pursuing this and that so as to
find time to sit in contemplation
Even the Buddha Shakyamuni had to practice zazen for six years [If] there are innumerable ways of understanding Buddhism, you should do
zazen alone In doing zazen it is desirable to have a quiet room.
You should stop pursuing words and letters and learn to withdraw and reflect on
yourself There is no reason to forsake your own sitting place and make futile trips
to other countries.
The way is completely present where you are Your tongue can be placed
against the roof of your mouth and your lips and teeth closed firmly. (2)
End a sitting session calmly
At the completion of zazen move your body slowly and stand up calmly. (3)
As you practice the sitting
contemplation, a way may open too (as you get along)
When you trace the source of the way, you find that it is universal and absolute.
Then sit firmly as a rock. 
Be temperate in eating and drinking.
Clothing should be loose but neat (convenient should do). (7)
Exert yourself in the way that points directly to your original Buddha nature (and)
the treasure house will then open of itself. So be able to enjoy it.
If you wish to realize the Buddha's wisdom, you should begin training at once
Ancient sages were so diligent, how can present-day trainees do without the practice
of zazen?
Learn to think beyond thinking and nonthinking. (rise mentally to that) No
distinction should be made between the clever and the stupid as you devote yourself
exclusively to and be completely absorbed in the practice of zazen.
Forsake all delusive relationships Sit upright [if you can] The
absolute way . . . is beyond enlightenment itself.
The way is, needless to say, very far from delusion. Why, then, be concerned about
the means of eliminating the latter? You know what is the most important thing in
Buddhism (Dogen calls it Zazen).
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.
- Stop pursuing this and that so as to find time to sit in contemplation.
- End a sitting session calmly. It should take a few minutes.
- As you practice the sitting contemplation, some way or ways may open too (as you
get along)
Find time to sit still a few minutes to let a way open up -

"Old Masters frequently warn: "Do not spend time wastefully" and "do not pass your time
in vain." Students today should begrudge every moment of time. This dewlike life fades away;
time speeds swiftly. In this short life of ours, avoid involvement in superfluous things and
just study the Way," said Dogen. [A Primer of Soto Zen, p. 83)
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