What is zazen good for?
The answer is simple:
Zazen isn't good for anything.
We are always looking for something. Some chase after money, others want love or sex. We study to get a good job, make a career and become a success. But in the end - what do we really want?
I think what we are really looking for is "happiness". We miss that feeling of being truly happy and satisfied. The crazy thing is that the more we chase after happiness, the farer away it seems to escape. Haven't we not only lost sight of happiness, but also of ourselves long ago?
The harder we try to be happy, the less we understand what happiness actually means. Have we forgotten that we actually have all we need in this moment? Maybe happiness isn't waiting for us somewhere "on the other side", but is right here and now?
Let's just stop for a moment. Stop chasing, stop running away. When you practice zazen, don't do it with the idea that you want to gain something. Just be yourself and sit. Let go and let zazen just be zazen. Then you will finally be just you - one.
An old Zen saying:
The practice of zazen is like a thief who breaks into an empty house: There is nothing to steal, nowhere to hide, and no-one to escape from.
Dôgen Zenji writes in the Zazengi:
"Sit solidly in concentration and think not-thinking. How do you do this? Let thoughts go! This is the art of zazen. It is not learning to do meditation. It is the dharma gate of great ease and joy. It is undefiled practice-realization."
Although zazen is described here as the gate of great ease and joy, more often than not you will experience pain, fatigue, anger, desire, greed, drowsiness, boredom, frustration, despair, and any other random thoughts. Let them all go.
If you do not sit with the determination to die, you will not be able to find the way of zazen. When you hold onto anything - even your own life - you will be just wasting your time.
Do not fight, just surrender to the posture. If you try to DO zazen, zazen will be far away. If you leave everything to the sitting posture itself, zazen will manifest naturally, automatically. Zazen must not be a tool for you, you have to give up yourself for zazen to realize itself.