So, what is the place of ... deep samadhi states in Shikantaza, the "Just Sitting Which Hits the Mark," the way of Zazen which is the centerpiece of Soto practice?
The answer is that we cherish and celebrate such states, honor ... and welcome samadhi when samadhi comes. However, we believe that samadhi which emerges from anything but an attitude of radical goallessness simply feeds the very hunger and thirst for gain that is the root of Dukkha suffering. It becomes one more pleasure and treasure to chase after and enjoy. It is this very hunt and hunger that we need to drop away in the grand equanimity and fulfillment of liberation.
So many schools of meditation make levels of concentration and spiritual attainment but more rungs to reach, finish lines to cross, payoffs to earn, prizes to stive for. It is literally "self-defeating," as the little self's very own hunger and hunting, reaching and striving is, in fact, the source of the very suffering from which it seeks relief.
Our solution to this dilemma in Shikantaza is to drop, to the marrow, all hunting and reaching, except for sitting itself for sitting's sake! Zazen must be good for nothing but sitting! Then, sitting itself is the treasure attained, sitting itself is the goal reached, all just by sitting. Without such radical goallessness and foresaking of all cravings for goals, meditation becomes another ploy to feed never ending, self-created feelings of human lack.
... For us Soto Zen folks, deep and pleasant samadhi will emerge in our Zazen, just as in the other schools of meditation, and it is wondrous! It is like an unsolicited treasure, for it arises right from our giving up of all need for finding, much like a door which unlocks only when we stop struggling to unlock it! The very act of dropping all need to turn the key leads to the door springing open! Such unsolicited samadhi is glorious!
In fact, EVERYTHING is glorious!
Everything is glorious because, in our equanimity, we equally honor and welcome as wondrous all the moments of Zazen without samadhi too! Both samadhi and the absence of samadhi are wondrous, and the total face of Zen samadhi! So many meditators make the mistake of thinking their meditation "good" only when they feel good and get what they want. In fact, Zazen is ALWAYS good ... both when it feels good and even when not, when we want just what we get.
Why?
It is something like saying that Shikantaza folks know the presence of the moon, not only on those clear and bright nights when the moon shines brightly, but also on the darkest and cloudiest nights. Only radical dropping of hunger to experience the moon can lead to a profound moon awareness which knows the moon both seen and unseen. We see the moon even on moonless nights, although not with the eyes. Then, on those cloudless evenings when the moon reveals itself in its fullness, and also on the nights when not, our trust is rewarded: The moon is always shining, seen or unseen.
Samadhi comes and samadhi goes, and we celebrate such coming and such going. True Zen samadhi is always present, whether come or gone, beyond coming and going.
So deep, this samadhi cannot be fathomed.