As to the zen-samadhi of the Mahayana,
There is just too much to praise.
What is Zen-samadhi?
In the Mahayana, meditation practice is technically called zen-samadhi (in Sanskrit, dhyana-samadhi), or the samadhi of meditation. In practical language it is simply called sitting zen (J. zazen) or sitting meditation. Zen-samadhi is the primary solution to the Buddhist question of the spiritual search. The historical Buddha realized enlightenment by sitting zen-samadhi, and as taught in the Parable of the Wayward Son in the True Dharma of the White Lotus Sutra, though Buddha preached and taught many truths, principles, and doctrines they all amounted to the skillful means of a wealthy father (Buddha) who wanted to return his lost and poor son (all beings) to his true inheritance to be gained by zen-samadhi. Thus all the words of Buddhism amount only to various means of convincing us to sit and meditate like Buddha did to realize enlightenment for oneself.
The difficulty of translating the Sanskrit term samadhi adequately into English is one reason the word has been used without translation and incorporated into English dictionaries. It is commonly, though erroneously, translated as “concentration”. Among the problems with the term “concentration” is that it is weighted too much on the “one pointedness” aspect of attention training which is only the beginning step of initial samadhi practice, and it creates the false impression that the whole of samadhi is the act of concentrating on a single object. A better translation would be “focus” in the sense that when awareness is concentrated on the focal point of awareness itself, rather than on a single object, then everything else (i.e., all things or ''dharmas'') comes into focus.
In the way that a camera or one’s eye does not reach out to things to bring them into focus and clarity but makes an inner adjustment of the focal point, so too, does the practice of zen-samadhi make an inner adjustment of the focal point of awareness. This inner adjustment is sometimes called “turning the light around” to draw attention to the fact that zen-samadhi does not reach out to focus on objects but turns inward to be aware of themeless or objectless awareness itself. Whether one is practicing zazen as “only minding doing sitting” (J. shikantaza) or as inquiry into “the source of speech” (Ch. huatou) with koans, the common denominator that makes them both zazen is that the zen-samadhi in the practice is not a concentration on an object but a themeless or formless focus on the focal point of awareness itself without the externalization of an object of form or thought used to act as a mediated object of awareness. Though “just sitting” zazen may start with concentration techniques such as focused breath counting or breath awareness and “koan inquiry” zazen may start with focused awareness of the focal point of the koan (e.g., a huatou such as “What is it?” or “Who hears?” or “Mu”) neither method of zazen becomes real zen-samadhi until the awareness is “turned around” from reaching out to objects to “focus” on the true suchness of awareness itself.
Another acceptable translation is “contemplation” in the sense of considering, observing, or noticing with steady attention. In Christian terminology contemplation can mean the state of mystical awareness of God’s being or the Godhead, which in Buddhist terminology would mean the direct awareness of the ground of being, that is, the Dharmakaya of the Tathagata.
From the etymological root of samadhi meaning “putting together,” “to join,” and “to combine,” other valid translations of samadhi are “union”, “unification”, and “absorbtion” in which all discriminations are joined or combined into a realization of the great non-dual harmony of true suchness.
Essentially, samadhi is the inherent state of steady or unperturbed awareness of one’s true nature. In the Platform Sutra Huineng describes zen-samadhi (i.e., the samadhi of meditation) in this way:
Learned and virtuous ones, what is called zen-samadhi (dhyana-samadhi)? Outwardly, to be free from characteristics is doing zen. Inwardly, to not be perturbed is doing samadhi. Outwardly, if one attaches to characteristics, inwardly, the heart-mind is immediately perturbed. Outwardly, if one is free from characteristics, the heart-mind is immediately not perturbed. The root nature by itself is pure, by itself is samadhi. Only by seeing conditions and thinking about conditions is one immediately perturbed. If someone sees various conditions and the heart-mind is not perturbed, this is real samadhi. Learned and virtuous ones, outwardly, to be free from characteristics is immediately zen. Inwardly, to not be perturbed is immediately samadhi. Outwardly, zen, inwardly, samadhi, this is doing zen-samadhi.
The Parable of the Lamp
In the Zen lineage of the Mahayana, the Three Trainings (or Threefold Learning, i.e., sila, samadhi, and prajna) are presented in the Parable of the Lamp using the ancient form of a lamp made up of a dish of oil with a lighted wick resting at the edge. The resting place of the table (or floor) is the body, the dish is the conscious mind, the oil is sila (moral conduct), the wick is samadhi (unperturbed contemplation), and the flame is prajna (intuitive wisdom). That which is called a "lamp" does not exist without all of the parts present and functioning. If there is no oil, then the wick is dry and the flame won't stay lit. If there is no wick, then there is nothing for the flame to be centered upon and anchored to. If there is no flame, then it is not actually a lamp but just a bowl of oil with a piece of string in it. The wick of samadhi does not become a true wick until it is lit with the flame of prajna, and the flame has no ability to combust until it has a wick through which to draw oil.
Of course metaphors can only be taken so far, but in line with this mutual identity of wick and flame, that is, the physical lamp and it's light, Huineng taught in Chapter 4 of the Platform Sutra that samadhi and prajna are essentially not different:
"Learned and virtuous ones, In this Dharma door of ours samadhi and prajna are considered to be the root. Great assembly, do not be confused. The words “samadhi” and “prajna” are different, but samadhi and prajna are one substance and are not two. Samadhi is the substance of prajna; prajna is the function of samadhi. Immediately at the time of prajna, samadhi is in prajna. Immediately at the time of samadhi, prajna is in samadhi. If one knows this meaning, then samadhi and prajna are equally learned. You various people who study the Way, do not say, 'First samadhi, then comes prajna,' or 'First prajna, then comes samadhi,' to separate them. Those with this view make the Dharma have the characteristic of duality."
Having begun with Hakuin's mention of zen-samadhi and then gone back to Huineng speaking about zen-samadhi, let us go further back to Bodhidharma, the man who brought the Ekayana Zen lineage to China. In the treatise titled "Great Master Dharma's Discourse on the Nature of Awakening" (達磨大師悟性論) Bodhidharma discusses zazen and zen-samadhi in what appears to be a direct foundation for Huineng's teaching. Here's the passage:
If a person knows that the six roots (i.e., 6 sense organs) are not real and the five accumulations (skandhas) are provisional names and that always to go seeking it in the body is necessarily to dwell without samadhi, then one should know that such a person expounds the words of the Buddha. A sutra says, "A home in the cave of the five accumulations is called the courtyard of zen. When the inner illumination is opened and unbound, then the gate of the Great Vehicle could not be brighter!"
` Not recollecting all things (sarvadharma), therefore, is called doing zen-samadhi. If someone understands these words, then walking, standing, sitting, and lying down are all zen-samadhi. Knowing the mind is empty is called the act of seeing Buddha. What is considered the reason? For all Buddhas in the 10 directions, in every consideration there is no mind. Not seeing in the mind, is called the act of seeing Buddha.
To unstingily renounce the body is called Great Charity (Skt. mahadana). The samadhi of detaching from the various activities is called Great Sitting Meditation (J. dai zazen). Because why? Worldly people are singly directed toward activities, and the Small Vehicle is singly directed toward samadhi. Namely, to pass beyond the worldly people and the sitting meditation (zazen) of the Small Vehicle is called the Great Sitting Meditation. If those who act with this realization, in all the various appearances, do not seek to release themselves and, in all the various illnesses, do not cure their own errors, then this is entirely the power of Great Zen-Samadhi.
So, as taught by Bodhidharma, Huineng, and Hakuin, the realization of zen is zen-samadhi. Everything that zen teachers have to say is nothing more than the great tapestry of brocade used to guide students to the realization of zen-samadhi.