From "Zen Mind, Beginner's Mind: Informal talks on Zen meditation and practice," which is a small compilation of Shunryu Suzuki's lectures assembled by one of his disciples, Trudy Dixon. (Weatherhill, 1970)
"When we practice zazen our mind always follows our breathing. When we inhale, the air comes into the inner world. When we exhale, the air goes out to the outer world. The inner world is limitless, and the outer world is also limitless. We say 'inner world' or 'outer world,' but actually there is just one whole world. In this limitless world, our throat is like a swinging door. The air comes in and goes out like someone passing through a swinging door. If you think, 'I breathe,' the 'I' is extra. There is no you to say 'I.' What we call 'I' is just a swinging door which moves when we inhales and when we exhale. It just moves; that is all. When your mind is pure and calm enough to follow this movement, there is nothing: no 'I,' no world, no mind nor body; just a swinging door.
"So when we practice zazen, all that exists is the movement of the breathing, but we are aware of this movement. You should not be absent-minded. But to be aware of the movement doe snot mean to be aware of your small self, but rather of your universal nature, or Buddha nature. This kind of awareness is very important, because we are usually so one-sided. Our usual understanding of life is dualistic: you and I, this and that, good and bad. But actually these discriminations are themselves the awareness of the universal existence. 'You' means to be aware of the universe in the form of you, and 'I' means to be aware of it in the form of I. You and I are just swinging doors. This kind of understanding is necessary. This should not even be called understanding, it is actually the true experience of life through Zen practice. ...
"All that we should do is just do something as it comes. Do something! Whatever it is, we should do it, even if it is not-doing something. We should live in this moment. So when we sit we concentrate on our breathing, and we become a swinging door, and we do something we should do, something we must do. This is Zen practice. In this practice there is no confusion. If you establish this kind of life you have no confusion whatsoever."
"Tozan, a famous Zen master, said, 'The blue mountain is the father of the white cloud. The white cloud is the son of the blue mountain. All day long they depend on each other, without being dependent on each other. The white cloud is always the white cloud. The blue mountain is always the blue mountain.' This is a pure, clear interpretation of life. There may be many things like the white cloud and blue mountain: man and woman, teacher and disciple. They depend on each other. But the white cloud should not be bothered by the blue mountain. The blue mountain should not be bothered by the white cloud. They are quite independent, but yet dependent. This is how we live, and how we practice zazen.
"When we become truly ourselves, we just become a swinging door, and we are purely independent of, and at the same time, dependent up on everything. Without air, we cannot breathe. Each one of us is in the midst of myriads of worlds. We are in the center of the world always, moment after moment. So we are completely dependent and independent. If you have this kind of experience, this kind of existence, you have absolute independence; you will not be bothered by anything. So when you practice zazen, your mind should be concentrated on your breathing. This kind of activity is the fundamental activity of the universal being. Without this experience, this practice, it is impossible to attain absolute freedom."