When you practice zazen you should not try to attain anything. You should just sit in the complete calmness of your mind and not rely on anything. Just keep your body straight without leaning over or against something. To keep your body straight means not to rely on anything. In this way, physically and mentally, you will obtain complete calmness. But to rely on something or try to do something in zazen is dualistic and not complete calmness.
If you want to study Zen, you should forget all your previous ideas and just practice zazen and see what kind of experience you have in your practice. That is naturalness.
Zazen practice is a direct expression of our true nature. Strictly speaking, for a human being, there is no other practice than this practice; there is no other way of life than this way of life.
When you are practicing zazen, do not try to stop your thinking. Let it stop by itself. If something comes into your mind, let it come in, and let it go out. It will not stay long. When you try to stop your thinking, it means you are bothered by it. Do not be bothered by anything. It appears as if something comes from outside your mind, but actually it is only the waves of your mind, and if you are not bothered by the waves, gradually they will become calmer and calmer.
When you say, “whatever I do is Buddha nature, so it doesn’t matter what I do, and there is no need to practice zazen,” that is already a dualistic understanding of our everyday life. If it really does not matter, there is no need for you even to say so. As long as you are concerned about what you do, that is dualistic.
For the beginner, practice without effort is not true practice. For the beginner, the practice needs great effort.
You become discouraged with your practice when your practice has been idealistic. You have some gaining idea in your practice, and it is not pure enough. It is when your practice is rather greedy that you become discouraged with it. So you should be grateful that you have a sign or warning signal to show you the weak point in your practice. At that time, forgetting all about your mistake and renewing your way, you can resume your original practice. This is a very important point.
Another mistake will be to practice for the sake of the joy you find in it. Actually, when your practice is involved in a feeling of joy, it is not in very good shape either. Of course it is not poor practice, but compared to the true practice it is not so good. In Hinayana Buddhism, practice is classified in four ways. The best way is to just do it without having any joy in it, not even physical joy. This way is just to do it, forgetting your physical and mental feeling, forgetting all about yourself in your practice. This is the fourth stage, the highest stage. The next highest stage is to have just physical joy in your practice. At this stage you find some pleasure in practice, and you will practice because of the pleasure you find in it. In the second stage you have both mental and physical joy, or good feeling. These two middle stages are stages in which you practice zazen because you feel good in your practice. The first stage is when you have no thinking and no curiosity in your practice. These four stages also apply to Mahayana practice, and the highest is just to practice it.