Jhana is a meditative state of profound stillness and concentration in which the mind becomes fully immersed and absorbed in the chosen object of attention. It is the cornerstone in the development of Right Concentration.
"There is the case where a monk — quite withdrawn from sensuality, withdrawn from unskillful qualities — enters and remains in the first jhana: rapture and pleasure born from withdrawal, accompanied by directed thought and evaluation. He permeates and pervades, suffuses and fills this very body with the rapture and pleasure born from withdrawal. There is nothing of his entire body unpervaded by rapture and pleasure born from withdrawal.
"Just as if a skilled bathman or bathman's apprentice would pour bath powder into a brass basin and knead it together, sprinkling it again and again with water, so that his ball of bath powder — saturated, moisture-laden, permeated within and without — would nevertheless not drip; even so, the monk permeates, suffuses and fills this very body with the rapture and pleasure born of withdrawal. There is nothing of his entire body unpervaded by rapture and pleasure born from withdrawal...
"Furthermore, with the stilling of directed thought and evaluation, he enters and remains in the second jhana: rapture and pleasure born of composure, unification of awareness free from directed thought and evaluation — internal assurance. He permeates and pervades, suffuses and fills this very body with the rapture and pleasure born of composure. There is nothing of his entire body unpervaded by rapture and pleasure born of composure.
"Just like a lake with spring-water welling up from within, having no inflow from east, west, north, or south, and with the skies periodically supplying abundant showers, so that the cool fount of water welling up from within the lake would permeate and pervade, suffuse and fill it with cool waters, there being no part of the lake unpervaded by the cool waters; even so, the monk permeates and pervades, suffuses and fills this very body with the rapture and pleasure born of composure. There is nothing of his entire body unpervaded by rapture and pleasure born of composure...
"And furthermore, with the fading of rapture, he remains in equanimity, mindful and alert, and physically sensitive to pleasure. He enters and remains in the third jhana, of which the Noble Ones declare, 'Equanimous and mindful, he has a pleasurable abiding.' He permeates and pervades, suffuses and fills this very body with the pleasure divested of rapture, so that there is nothing of his entire body unpervaded with pleasure divested of rapture.
"Just as in a blue-, white-, or red-lotus pond, there may be some of the blue, white, or red lotuses which, born and growing in the water, stay immersed in the water and flourish without standing up out of the water, so that they are permeated and pervaded, suffused and filled with cool water from their roots to their tips, and nothing of those blue, white, or red lotuses would be unpervaded with cool water; even so, the monk permeates and pervades, suffuses and fills this very body with the pleasure divested of rapture. There is nothing of his entire body unpervaded with pleasure divested of rapture...
"And furthermore, with the abandoning of pleasure and stress — as with the earlier disappearance of elation and distress — he enters and remains in the fourth jhana: purity of equanimity and mindfulness, neither-pleasure-nor-pain. He sits, permeating the body with a pure, bright awareness, so that there is nothing of his entire body unpervaded by pure, bright awareness.
"Just as if a man were sitting wrapped from head to foot with a white cloth so that there would be no part of his body to which the white cloth did not extend; even so, the monk sits, permeating his body with a pure, bright awareness. There is nothing of his entire body unpervaded by pure, bright awareness."
"I declare a person endowed with four qualities to be one of great discernment, a great man. Which four?
"There is the case, brahman, where he practices for the welfare & happiness of many people and has established many people in the noble method, i.e., the rightness of what is admirable, the rightness of what is skillful.
"He thinks any thought he wants to think, and doesn't think any thought he doesn't want to think. He wills any resolve he wants to will, and doesn't will any resolve he doesn't want to will. He has attained mastery of the mind with regard to the pathways of thought.
"He attains — whenever he wants, without strain, without difficulty — the four jhanas that are heightened mental states, pleasant abidings in the here-&-now.
"With the ending of mental fermentations — he remains in the fermentation-free awareness-release & discernment-release, having directly known & realized them for himself right in the here-&-now.
"...I declare a person endowed with these four qualities to be one of great discernment, a great man."
There's no jhana for one with no discernment, no discernment for one with no jhana. But one with both jhana & discernment: he's on the verge of Unbinding.