Soto Zen folks say that every moment of Zazen is complete, sacred, a perfect action, with not one thing to add, not one thing to take away. When we sit Zazen, we are a Buddha sitting. In such way, we come to taste all of this life and world as sacred, a jewel, with not one thing to add, not one thing to take away from it. Perfectly just-what-it-is.
But we have to be very cautious here, not misunderstand:
... Saying “we are already Buddha” is not enough if we don’t realize that, act like so!
Simple, exaggerated example …
Perhaps a fellow sits down to Zazen for the first time who is a violent man, a thief and alcoholic. He hears that “all is Buddha just as it is“, so thinks that Zen practice means “all is a jewel just as it is, so thus maybe I can simply stay that way, just drink and beat my wife and rob strangers“. Well, no, because while a thief and wife-beater is just that … a thief and wife-beater, yet a Buddha nonetheless … still, someone filled with such anger and greed and empty holes to fill in their psyche is not really “at peace with how things are” (or he would not beat and steal and need to self-medicate). In other words, he takes and craves and acts from anger and frustration because he does not truly understand “peace with this life as it is” … because if he did, he would not need to be those violent, punishing ways.
If the angry, violent fellow truly knew “completeness“, truly had “no hole in need of filling“, “nothing lacking” everything “complete just as it is” … well, he simply would not have need to do violence, stealing and take drugs to cover his inner pain.
This is a non-self-fulfilling Catch-22.