From Mushin:
Making a wholehearted effort or diligence is another of Dogen Zenji’s Eight Awakenings of Great Beings. Anybody who follows the Buddhadharma with sincere intention to live it out, to embody its wisdom, learns how to live steadily and completely. You embody this when you sit zazen with your entire body and mind, all the way through, realizing the meaning of no body, no mind. Diligent effort doesn’t yield anything you don’t already have. In this way there really is nothing to accomplish through practice, nothing to gain, though we usually believe when we start out that there is something missing that practice will gain for us.
Our usual way of living is to take an action with the intention to accomplish something. But all you take up in Zen practice is to accomplish your true life. Just as every day is fully lived, every breath is natural. You don’t have to think about it to be so. When you practice with diligence as we’re pointing to here, you exactly live out your whole self, without comparing to some idea or matching some ideal that you think is better. This is a subtle and deep teaching Dogen is reminding us of. Diligence, not tension. Diligence, steady and with your whole body and mind.