​MN 30 Culasaropama Sutta: The Shorter Discourse on the Simile of the Heartwood 

Thus have i heard.

On one occasion the Blessed One was living at Savatthi in Jeta's Grove, Anathapindika's Park. Then the brahmin Pingalakoccha went to the Blessed One and exchanged greetings with him. When this courteous and amiable talk was finished, he sat down at one side and said to the Blessed One: "Master Gotama, there are these recluses and brahmins, each the head of an order, the head of a group, the teacher of a group, a well-known and famous founder of a sect regarded by many as a saint; they are Purana Kassapa, Makkhali Gosala, Ajita Kesakambalin, Pakudha Kaccayana, Sanjaya Belatthiputta, and the Nigantha Nataputta. They all claimed to have direct knowledge but do some of them had direct knowledge or none ?"
Buddha:"Enough, brahmin! Put this question aside. I will teach you the Dhamma. Listen and pay close attention. I will speak." 
"Yes, sir," the brahmin Pingalakoccha replied.

The Blessed One said this: "Suppose, brahmin, a man needing heartwood, seeking heartwood, wandering in search of heartwood, came to a great tree standing possessed of heartwood. Passing over its heartwood, its sapwood, its inner bark, and its outer bark, he would cut off its twigs and leaves and take them away thinking they were heartwood. Then a man with good sight, seeing him, might say: 'This good man did not know the heartwood, the sapwood, the inner bark, the outer bark, or the twigs and leaves. Thus, while needing heartwood, seeking heartwood, wandering in search of heartwood, he came to a great tree standing possessed of heartwood, and passing over its heartwood, its sapwood, its inner bark, and its outer bark, he cut off its twigs and leaves and took them away thinking they were heartwood. Whatever it was this good man had to make with heartwood, his purpose will not be served.'

"Suppose a man needing heartwood, wandering in search of heartwood, came to a great tree standing possessed of heartwood. Passing over its heartwood, its sapwood and its inner bark, he would cut off its outer bark and take it away thinking it was heartwood. Then a man with good sight, seeing him, might say: 'This good man did not know the heartwood...or the twigs and leaves. Thus, while needing heartwood...he cut off its outer bark and took it away thinking it was heartwood. Whatever it was this good man had to make with heartwood, his purpose will not be served.'

"Suppose a man needing heartwood, seeking heartwood came to a great tree standing possessed of heartwood. Passing over its heartwood and its sapwood, he would cut off its inner bark and take it away thinking it was heartwood. Then a man with good sight, seeing him, might say: 'This good man did not know the heartwood...or the twigs and leaves. Thus, while needing heartwood...he cut off its inner bark and took it away thinking it was heartwood. Whatever it was this good man, had to make with heartwood, his purpose will not be served.'

"Suppose a man needing heartwood, seeking heartwood came to a great tree standing possessed of heartwood. Passing over its heartwood, he would cut off its sapwood and take it away thinking it was heartwood. Then a man with good sight, seeing him, might say: 'This good man did not know the heartwood.. .or the twigs and leaves. Thus, while needing heartwood...he cut off its sapwood and took it away thinking it was heartwood. Whatever it was this good man had to make with heartwood, his purpose will not be served.'
​"Suppose a man needing heartwood, seeking heartwood came to a great tree standing possessed of heartwood, and cutting off only its heartwood, he would take it away knowing it was heartwood. Then a man with good sight, seeing him, might say: 'This good man knew the heartwood, the sapwood, the inner bark, the outer bark, and the twigs and leaves. Thus, while needing heartwood, he came to a great tree standing possessed of heartwood, and cutting off only its heartwood, he took it away knowing it was heartwood. Whatever it was this good man had to make with heartwood, his purpose will be served.'

​"Similarly brahmin, here some clansman goes forth out of faith from the home life into homelessness, considering: 'I am a victim of birth, ageing, and death, of sorrow, lamentation, pain, grief, and despair; I am a victim of suffering, a prey to suffering. Surely an ending of this whole mass of suffering can be known.' When he has gone forth thus, he acquires gain, offerings and fame. He is pleased with that gain, offerings and fame, and his intention is fulfilled. On account of it he lauds himself and disparages others thus: 'I have gain, offerings and fame, but these other bhikkhus are unknown, of no account.' So he arouses no desire to act, he makes no effort for the realization of those other states that are higher and more sublime than gain, offerings and fame; he hangs back and slackens. I say that this person is like the man needing heartwood, who came to a great tree standing possessed of heartwood, and passing over its heartwood, its sapwood, its inner bark, and its outer bark, cut off its twigs and leaves and took them away thinking they were heartwood; and so whatever it was he had to make with heartwood, his purpose will not have been served."

"Here, brahmin, some clansman goes forth out of faith from the home life into homelessness, considering: 'I am a victim of birth, ageing, and death, of sorrow, lamentation, pain, grief, and despair; I am a victim of suffering, a prey to suffering. Surely an ending of this whole mass of suffering can be known.' When he has gone forth thus, he acquires gain, offerings and fame. He is not pleased with that and his intention is not fulfilled. He does not, on account of it, laud himself and disparage others. He arouses desire to act and he makes an effort for the realization of those other states that are higher and more sublime than gain, honor, and renown; he does not hang back and slacken. He achieves the attainment of virtue. He is pleased with that attainment of virtue and his intention is fulfilled. On account of it he lauds himself and disparages others thus: 'I am virtuous, of good character, but these other bhikkhus are immoral, of evil character.' So he arouses no desire to act, he makes no effort for the realization of those other states that are higher and more sublime than the attainment of virtue; he hangs back and slackens. His purpose will not have been served.   
​"Here, brahmin, some clansman goes forth out of faith from the home life into homelessness, considering: 'I am a victim of birth, ageing, and death, of sorrow, lamentation, pain, grief, and despair; I am a victim of suffering, a prey to suffering. Surely an ending of this whole mass of suffering can be known.' When he has gone forth thus, he acquires gain, honour, and renown. He is not pleased with that and his intention is not fulfilled. He achieves the attainment of virtue. He is pleased with that attainment of virtue, but his intention is not fulfilled. He does not, on account of it, laud himself and disparage others. He arouses desire to act and he makes an effort for the realization of those other states that are higher and more sublime than,the attainment of virtue; he does not hang back and slacken. He achieves the attainment of concentration. He is pleased with that attainment of concentration and his intention is fulfilled. On account of it he lauds himself and disparages others thus: 'I am concentrated, my mind is unified, but these other bhikkhus are unconcentrated, with their minds astray.' So he arouses no desire to act, he makes no effort for the realisation of those other states that are higher and more sublime than the attainment of concentration; he hangs back and slackens. I say that this person is like the man needing heartwood... passing over its heartwood and its sap wood, cut off its inner bark and took it away thinking it was heartwood; and so whatever it was he had to make with heartwood, his purpose will not have been served." 

​"Here, brahmin, some clansman goes forth out of faith from the home life into homelessness, considering: 'I am a victim of birth, ageing, and death, of sorrow, lamentation, pain, grief, and despair; I am a victim of suffering, a prey to suffering. Surely an ending of this whole mass of suffering can be known.' When he has gone forth thus, he acquires gain, honour, and renown. He is not pleased with that and his intention is not fulfilled...He achieves the attainment of virtue. He is pleased with that attainment of virtue, but his intention is not fulfilled...He achieves the attainment of concentration. He is pleased with that attainment of concentration, but his intention is not fulfilled. He does not, on account of it, laud himself and disparage others. He arouses desire to act and he makes an effort for the realization of those other states that are higher and more sublime than the attainment of concentration; he does not hang back and slacken. He achieves knowledge and vision. He is pleased with that knowledge and vision and his intention is fulfilled. On account of it he lauds himself and disparages others thus: 'I live knowing and seeing, but these other bhikkhus live unknowing and unseeing.' So he arouses no desire to act, he makes no effort for the realization of those other states that are higher and more sublime than knowledge and vision; he hangs back and slackens. I say that this person is like the man needing heartwood...who passing over its heartwood, cut off its sapwood and took it away thinking it was heartwood; and so whatever it was he had to make with heartwood, his purpose will not have been served."

"Here, brahmin, some clansman goes forth out of faith from the home life into homelessness, considering: 'I am a victim of birth, ageing, and death, of sorrow...; I am a victim of suffering, a prey to suffering. Surely an ending of this whole mass of suffering can be known.' When he has gone forth thus,he acquires gain, honor, and renown. He is not pleased with that and his intention is not fulfilled...He achieves the attainment of virtue. He is pleased with that attainment of virtue, but his intention is not fulfilled...He achieves the attainment of concentration. He is pleased with that attainment of concentration, but his intention is not fulfilled...He achieves knowledge and vision. He is pleased with that knowledge and vision, but his intention is not fulfilled. He does not, on account of it, laud himself and disparage others. He arouses desire to act and he makes an effort for the realization of those other states that are higher and more sublime than knowledge and vision he does not hang back and slacken. "
​"But what, brahmin, are the states that are higher and more sublime than knowledge and vision? Here, brahmin, quite secluded from sensual pleasures, secluded from unwholesome states, a bhikkhu enters upon and abides in the first jhana, which is accompanied by applied and sustained thought, with rapture and pleasure born of seclusion. This is a state higher and more sublime than knowledge and vision. Again, with the stilling of applied and sustained thought, a bhikkhu enters upon and abides in the second jhana, which has self-confidence and singleness of mind without applied and sustained thought, with rapture and pleasure born of concentration. This too is a state higher and more sublime than knowledge and vision. Again, with the fading away as well of rapture, a bhikkhu abides in equanimity, and mindful and fully aware, still feeling pleasure with the body, he enters upon and abides in the third jhana, on account of which noble ones announce: 'He has a pleasant abiding who has equanimity and is mindful.' This too is a state higher and more sublime than knowledge and vision. "

"Again, with the abandoning of pleasure and pain, and with the previous disappearance of joy and grief, a bhikkhu enters upon and abides in the fourth jhana, which has neither-pain-nor pleasure and purity of mindfulness due to equanimity. This too is a state higher and more sublime than knowledge and vision. Again, with the complete surmounting of perceptions of form, with the disappearance of perceptions of sensory impact, with non-attention to perceptions of diversity, aware that 'space is infinite', a bhikkhu enters upon and abides in the base of infinite space. This too is a state higher and more sublime than knowledge and vision. Again, by completely surmounting the base of infinite space, aware that 'consciousness is infinite/ a bhikkhu enters upon and abides in the base of infinite consciousness. This too is a state higher and more sublime than knowledge and vision. Again, by completely surmounting the base of infinite consciousness, aware that 'there is nothing,' a bhikkhu enters upon and abides in the base of nothingness. This too is a state higher and more sublime than knowledge and vision.

"Again, by completely surmounting the base of nothingness, a bhikkhu enters upon and abides in the base of neither perception-nor-non-perception. This too is a state higher and more sublime than knowledge and vision. Again, by completely surmounting the base of neither perception-nor-non-perception, a bhikkhu enters upon and abides in the cessation of perception and feeling. And his taints are destroyed by seeing with wisdom. This too is a state higher and more sublime than knowledge and vision. These are the states that are higher and more sublime than knowledge and vision. "

"I say that this person, brahmin, is like a man needing heartwood, seeking heartwood,who came to a great tree standing possessed of heartwood, and cutting off its heartwood, took it away knowing it was heartwood; and so whatever it was he had to make with heartwood, his purpose will have been served. "

"So this holy life, brahmin, does not have gain, honor, and renown for its benefit, or the attainment of virtue or the attainment of concentration or knowledge and vision for its benefit. But it is this un-shake-able deliverance of mind that is the goal of this holy life, its heartwood, and its end."

When this was said, the brahmin Pingalakoccha said to the Blessed One: "Magnificent, Master Gotama! Magnificent, Master Gotama! Master Gotama has made the Dhamma clear in many ways, as though he were turning upright what had been overthrown, revealing what was hidden, showing the way to one who was lost, or holding up a lamp in the dark for those with eyesight to see forms. I go to Master Gotama for refuge and to the Dhamma and to the Sangha of bhikkhus. From today let Master Gotama remember me as a lay follower who has gone to him for refuge for life." 
In summary, these two discourses MN 29-30 emphasise that the proper goal of the holy life is the unshakeable deliverance of the mind, to which all other benefits are subsidiary.It illustrates a simile given by the Buddha. A man sets out searching for heartwood, but mistaking the leaves and twigs for heartwood, he carries them off thinking they are the heartwood. It is used to illustrate how a man setting out to find Awakening who settles for gains, honors and reputation instead (wrong path). Similarly the other layers of a tree are used to describe a seeker who settles for less than the heartwood: accomplishment in virtue, concentration and knowledge & wisdom. In each of these cases the man is declared to be ignorant both of the thing he has accomplished and the final goal. Finally, the heartwood is presented as being the unshakable heart's release: final awakening, liberation, nibbana. 
​References: 
1. www.accesstoinsight.org
2. https://suttacentral.net/
3. The middle length discourses of the Buddha (Bhikkhu Bodhi)