Mental Development
Monks, although a monk who does not apply himself to the meditative development of his mind may wish, “Oh, that my mind might be freed from the taints by non-clinging!,” yet his mind will not be freed. For what reason? “Because he has not developed his mind,” one has to say. Not developed it in what? In the four foundations of mindfulness, the four right kinds of striving, the four bases of success, the five spiritual faculties, the five spiritual powers, the seven factors of enlightenment and the Noble Eightfold Path.
Suppose, monks, a hen has eight, ten or twelve eggs, but she does not sit on them sufficiently long and they are not well warmed, not developed enough for hatching. Alhough that hen may wish, “Oh, that my chicks might break the egg shells with their claws and beaks and emerge safely!,” yet these chicks will not be able to do so. For what reason? Because the hen did not sit on the eggs sufficiently long, so that they are not well warmed and developed enough for hatching. Similarly is it with a monk who has not applied himself to the meditative development of his mind.
If, however, a monk has applied himself to the meditative development of his mind, even if he should not wish, “Oh, that my mind might be freed from the taints by non-clinging!,” still his mind will be freed. For what reason? “Because he has developed his mind,” one has to say. Developed it in what? In the four foundations of mindfulness, the four right efforts, the four bases of success, the five spiritual faculties, the five spiritual powers, the seven factors of enlightenment and the Noble Eightfold Path.
Suppose, monks, a hen has eight, ten or twelve eggs, and she has sat on them sufficiently long, so that they are well warmed and developed enough for hatching. Even if that hen did not wish, “Oh, that my chickens might break the egg shells with their claws and beaks and emerge safely!,” still the chicks will break through the shells and emerge safely. For what reason? Because the hen sat on the eggs sufficiently long, so that they are well warmed and developed enough for hatching. Similarly is it with a monk who has applied himself to the meditative development of his mind.
Suppose, monks, a carpenter has an axe and its handle shows the marks of his fingers and thumb. He will not know that so much of the handle has worn away today, so much yesterday and so much at other times; but he will just know of what is wasted that it has worn away. It is similar with a monk who applies himself to the meditative development of his mind: though he has no knowledge that so much of the taints has worn away today, so much yesterday and so much at other times, yet he knows of what is wasted that it is worn away.
Or suppose, monks, an ocean-going boat rigged with ropes, having been exposed to the water for six months, has been dragged to the shore for the winter. Then the ropes that had been affected by wind and sun, when soaked by the monsoon rains, will easily go to waste and rot away. It is similar with a monk who applies himself to the meditative development of his mind: his fetters will easily be loosened and rot away.
(7:67)
https://www.urbandharma.org/pdf1/wh2...araNikaya2.pdf