I believe that the answers to these questions can be found in Bendowa, the first fascicle in Dogen's Shobogenzo. It contains a section that consists of Q/A from various students. I am going to post from an online translation I found (http://www.zenki.com/index.php?lang=en&page=bendo01
), but I prefer the Nishijima-Cross version, and advise you to obtain that copy instead (http://www.amazon.com/Master-Dogens-Sho ... 0952300214
). Also, as Dogen can be rather cryptic at times, it is nice to hear a modern-day teacher's explanations of his writings. I will cautiously recommend Brad Warner's writings, particularly Sit Down and Shut Up (http://www.amazon.com/Sit-Down-Shut-Up-Commentaries/dp/1577315596
). Although he maintains many heterodox views on Buddhism, I feel that he has done the best job to interpret Dogen in modern writing that I am aware of.
Why worry about seated meditation so much? Why exclude the other enlightened activities?
This one is actually presented as several questions in Bendowa, so this will be lengthy.
Q: I have heard of the superior merits of zazen. But an ordinary person will have doubts and say there are many gates in Buddhism. Why do you urge only zazen?
A: Because it is the right gate to Buddhism - this is my answer to him.
Q: Why is it the only right gate?
A: The great teacher Sakyamuni handed down this unexcelled method of enlightenment. And the Tathagatas of the past, present, and future were similarly enlightened by zazen. They, too, transmitted it as the right gate. The patriarchs in India and China were also enlightened by zazen. For this reason, I now indicate the right gate for human beings and heaven.
Q: Such reasons as correct transmissioby the unexcelled method of the Tathagatas and following in the footsteps of the patriarchs are beyond common sense. To ordinary people, reading the sutra and saying the Nembutsu are the natural means to enlightenment. You just sit cross-legged and do nothing. How is this a means to enlightenment?
A: You look on the meditation of the Buddhas and the supreme law as just sitting and doing nothing. You disparage Mahayana Buddhism. Your delusion is deep; you are like someone in the middle of the ocean crying out for water. Fortunately we are already sitting at ease in the self-joyous meditation of the Buddhas. Isn't this a great boon? What a pity that your true-eye remains shut-that your mind remains drunk. The world of the Buddhas eludes ordinary thinking and consciousness. It cannot be known by disbelief and inferior knowledge. To enter one must have right belief. The disbeliever, even if taught, has trouble grasping it. For example, when the Buddha was preaching at Grdhrakuta, the disbelieves were allowed to go away. To bring out the right belief in your mind you must train and study. If you cannot do this, you should quit for awhile, regretting that you lack the influence of the law from a former beneficial relation. What good are such actions as reading the sutras and saying the Nembutsu. How futile to think that Buddhist merits accrue from merely moving the tongue and raising the voice. If you think this covers Buddhism, you are far from the truth. Your only purpose in reading the sutras should be to learn thoroughly that the Buddha taught the rules of gradual and sudden training and that by practicing his teachings you can obtain enlightenment. You should not read the sutras merely to pretend to wisdom through vain intellections. To strive for the goal of Buddhism by reading many sutras is like pointing the hill to the north and heading south. It is like putting a square peg in a round hole. While you look at words and phrases, the path of your training remains dark. This is as worthless as a doctor who forgets his prescription. Constant repetition of the Nembutsu is also worthless-like a frog in a spring field croaking night and day. Those deluded by fame and fortune, find it especially difficult to abandon the nembutsu. Bound by deep roots to a profit-seeking mind, they existed in ages past, and they exist today. They are to be pitied. Understand only this: if enlightened Zen masters and their earnest disciples correctly transmit the supreme law of the seven Buddhas, its essence emerges, and it can be experienced. Those who merely study the letters of the sutras cannot know this. So put a stop to this doubt and delusion. Follow the teachings of a real master and, by zazen; attain to the self-joyous samadhi of the Buddhas.
Q: Why does Buddhism advocate meditation and enlightenment through cross-legged sitting alone (of the four actions)?
A: I do not analyze the way of training and enlightenment followed by the various Buddhas. If you ask why, I say simply that it is the way used in Buddhism. You should not seek no further. But the patriarchs praised cross-legged sitting, calling it the comfortable way. I know this sitting is the most comfortable of the four actions. It is not only the training of one Buddha or two Buddhas but of all Buddhas and patriarchs.
Again, but since we are all enlightened already why the focus on Zazen? Although I can follow the logic I can't really see the connection.
Again, this question is directly addressed in Bendowa.
Q: Some people say that to know Buddhism you only have to understand the meaning of "this mind itself is the Buddha"; you do not have to chant the sutras or train the body in Buddhism. Understand only that Buddhism is inherent in your self - this is full enlightenment. There is no need for seeking anything from others. So is there any use going to the trouble of practicing zazen?
A: That is a most grievous error. If what you say is true - even though the sages teach this ("this mind itself is the Buddha") - you cannot understand it. To study Buddhism you have to transcend the viewpoint of self and others. If you become enlightened by knowing that the self itself is the Buddha, Sakyamuni long ago would not have tried so hard to teach the way. This is evident in the high standards of the ancient Zen masters. Long ago there was a monk named Tse-kung Chien-yuan under Zen master Fa-yen. Fa-yen asked him: Tse-kung, how long have you been in this monastery? Tse-kung answered: I have been here three years. Fa-yen: You are younger than me. Why don't you ever ask me about Buddhism? Tse-kung: I will not lie. While studying under Zen master Ch'ing-feng, I understood the serenity of Buddhism. Fa-yen: By what words did you gain this understanding? Tse-kung: I asked Ch'ing-feng, What is the real self of the trainee? He answered, The God of Fire calls for fire. Fa-yen: That's a fine expression. But you probably did not understand it. Tse-kung: The God of Fire belongs to fire. Fire needs fire. It is like saying that the self needs the self. This is how I understood it. Fa-yen: I see clearly that you did not understand. If Buddhism is like that, it would not have continued until now. This disturbed Tse-kung deeply, and he left there. On the way home he thought: Fa-yen is an excellent Zen master and the leader of 500 disciples. He has pointed out my fault. There must be a valuable point in his words. Tse-kung then returned to Fa-yen's monastery. Repenting and giving his salutation, he asked: What is the real self of the trainee? Fa-yen answered: The God of Fire calls for fire. On hearing this, Tse-kung was fully enlightened about Buddhism. Obviously one does not know Buddhism by merely understanding that this self is the Buddha. If this is Buddhism, Fa-yen could not have guided Tse-kung in the manner described above, nor would he have given the advice he did. On first visiting a Zen master, you should ask for the rules of training. Only practice zazen earnestly and avoid cluttering your mind with superficial knowledge. The unexcelled method of Buddhism will then bear fruit.