This sutta contains a full presentation of the Eightfold Path, demonstrating a person progressing from novice to ultimate Nibbana. The translation is by Bhikhhu Bodhi in In the Buddha's Words. This sutta has multiple variant: MN 38, MN 39, MN 53, MN 107, and MN 125, as well as a longer version in DN 2. There is no doubt that this is an extremely important sutta.

Stage 0: Hearing the Dharma

1. “So too, brahmin, here a Tathāgata appears in the world, an arahant, perfectly enlightened, perfect in true knowledge and conduct, fortunate, knower of the world, unsurpassed leader of persons to be tamed, teacher of devas and humans, the Enlightened One, the Blessed One. Having realized with his own direct knowledge this world with its devas, Māra, and Brahmā, this population with its ascetics and brahmins, with its devas and humans, he makes it known to others. He teaches a Dhamma that is good in the beginning, good in the middle, and good in the end, with the right meaning and expression; he reveals a holy life that is perfectly complete and purified.

The sutta presents a view of the path that is circular: a Tathāgata appears and preaches the dharma, some being learns the dharma in this way, and then this being may embark on the path of the dharma, which may culminate in the being's awakening to become a new Tathāgata, and the cycle repeats.

The path is in fact not complicated, and nothing is preventing anyone from undertaking it. Many readers familiar with various advanced or elaborate teachings may in fact be struck by how simple it is. The primary factor is renunciation and discipline to adhere to clear instructions. Of course, pretty much all of humanity lacks those in sufficient measures (including yours truly), so nobody actually follows that.

If you follow this sutta, it is clear that a dedicated practitioner can indeed gain enlightenment in as little as 7 days, as the Buddha states in MN 10: Satipaṭṭhāna Sutta.

Stage 1: Moral Rectitude (Sila)

1. “A householder or householder’s son or one born in some other clan hears that Dhamma. On hearing the Dhamma he acquires faith in the Tathāgata.

No commentary necessary.

Now, in this forum I argued often in the past in favor of seclusion. For this intuitive conviction, I received harsh and often rude criticism from the various enlightened beings in this forum. Imagine my surprise to discover that the Buddha in fact entirely supports my position in this central sutta. Apparently, my critics are not enlightened at all, but mired in ignorance not just of the dharma, but even of explicit teachings:

Possessing that faith, he considers thus: ‘Household life is crowded and dusty; life gone forth is wide open. It is not easy, while living in a home, to lead the spiritual life utterly perfect and pure as a polished shell.

[...]

1. “He becomes content with robes to protect his body and with almsfood to maintain his stomach, and wherever he goes, he sets out taking only these with him. Just as a bird, wherever it goes, flies with its wings as its only burden, so too the monk becomes content with robes to protect his body and with almsfood to maintain his stomach, and wherever he goes, he sets out taking only these with him. Possessing this aggregate of noble moral discipline, he experiences within himself the bliss of blamelessness.

[...]

1. “Possessing this aggregate of noble moral discipline, and this noble restraint of the faculties, and possessing this noble mindfulness and clear comprehension, he resorts to a secluded resting place: the forest, the root of a tree, a mountain, a ravine, a hillside cave, a charnel ground, a jungle thicket, an open space, a heap of straw.

Our noble disciple is practicing in complete seclusion. Every morning, he meets some lay people who donate almsfood to his bowl. Following this brief interaction, there is no more mention of any human contact. The noble disciple "secludes" himself to an isolated location, such as a forest, a mountain, ravine, cave - anywhere far from others.

Clearly the Buddha was wrong to suggest this, for we are all enlightened in this forum, and realize the crucial importance of the sangha. If I had to guess, this was a later addition by some Theravadins who wanted to ensure Buddhism becomes a proper church with plenty of earthly power for them to enjoy.

Roaming free as a bird, carrying nothing with him, with perfect rectitude and no moral dangers - remarkably similar to the ethos of the wandering Chan master 1,200 years later.

It's important to note that this description is not limited to a "lone Buddha" (pratyekabuddha / paccekabuddha) or any similar exception; it is very clear from reading the sutta that is a normal path to enlightenment. I believe there are in fact enough similarities with the Buddha's own path, especially towards the end, to support a claim that the person hereby enlightened will become a full Buddha and teacher in his own right.

Sections 13-17 focus on the principles of moral discipline (sila) that most of us know already. There's the Five Precepts, plus the additional precepts that apply to renunciates. No need to repeat them here, but there are two interesting comment.

The basis for moral discipline is RESTRAINT

This cannot be overemphasized. The entire basis for the practice of moral discipline is deliberate restraint of the mind and body from unwholesome action:

1. “On seeing a form with the eye, he does not grasp at its signs and features.11 Since, if he left the eye faculty unguarded, evil unwholesome states of longing and dejection might invade him, he practices the way of its restraint, he guards the eye faculty, he undertakes the restraint of the eye faculty. On hearing a sound with the ear … On smelling an odor with the nose … On tasting a flavor with the tongue … On feeling a tactile object with the body … On cognizing a mental phenomenon with the mind, he does not grasp at its signs and features. Since, if he left the mind faculty unguarded, evil unwholesome states of longing and dejection might invade him, he practices the way of its restraint, he guards the mind faculty, he undertakes the restraint of the mind faculty. Possessing this noble restraint of the sense faculties, he experiences within himself an unsullied bliss.

In the past, I suggested restraint as a fundamental basis of practice, which incurred the wrath of the many noble Bodhisattvas inhabiting this forum, such as u/Trailokyavijaya who claimed that restraint will likely lead to "suppression" and thus be entirely unproductive. Well, far be it for me to argue against folks who are evidently more enlightened than the Buddha.

The second noteworthy aspect of this first stage of the path is that it also incorporates some initial mindfulness. Thus, while the path is simple, it is not entirely linear; while Right Mindfulness properly belongs in the 3rd stage (wisdom - Pranja) of the path, it is already crucial at this first stage, essential to the establishment of correct moral discipline:

1. “He becomes one who acts with clear comprehension when going forward and returning; who acts with clear comprehension when looking ahead and looking away; who acts with clear comprehension when flexing and extending his limbs; who acts with clear comprehension when wearing his robes and carrying his outer robe and bowl; who acts with clear comprehension when eating, drinking, chewing, and tasting; who acts with clear comprehension when defecating and urinating; who acts with clear comprehension when walking, standing, sitting, falling asleep, waking up, talking, and keeping silent.

When you think about it, it's impossible to exercise restraint from unwholesome states without having enough Right View to recognize these states at the very least. Moreover, some Right View is required to be inspired by the preaching of the Tathāgata and embark on the path at all. Thus, Right View is both the beginning of the path, as well as its end upon full realization, and pervades the path throughout.

Stage 2: Concentration (Samadhi)

1. “On returning from his almsround, after his meal he sits down, folding his legs crosswise, setting his body erect, and establishing mindfulness before him. Abandoning longing for the world, he dwells with a mind free from longing; he purifies his mind from longing. Abandoning ill will and hatred, he dwells with a mind free from ill will, compassionate for the welfare of all living beings; he purifies his mind from ill will and hatred. Abandoning dullness and drowsiness, he dwells free from dullness and drowsiness, percipient of light, mindful and clearly comprehending; he purifies his mind from dullness and drowsiness. Abandoning restlessness and remorse, he dwells free from agitation with a mind inwardly peaceful; he purifies his mind from restlessness and remorse. Abandoning doubt, he dwells having gone beyond doubt, unperplexed about wholesome states; he purifies his mind from doubt.

Our noble disciple thus engages in concentration (samadhi) meditation, which (temporarily) purifies his mind. He overcomes the Five Hindrances. He mind becomes sharp, pure, and concentrated. The attachments are still there, but they are shut out for the present.

Taken to the next level, this whole state matures into a jhana:

1. “Having thus abandoned these five hindrances, defilements of the mind that weaken wisdom, secluded from sensual pleasures, secluded from unwholesome states, he enters and dwells in the first jhāna, which is accompanied by thought and examination, with rapture and happiness born of seclusion.

Further deepening his concentrated absorption, he then attains the deeper jhanas:

1. “Again, with the subsiding of thought and examination, he enters and dwells in the second jhāna, which has internal confidence and unification of mind, is without thought and examination, and has rapture and happiness born of concentration.

[...]

1. “Again, with the fading away as well of rapture, he dwells equanimous and, mindful and clearly comprehending, he experiences happiness with the body; he enters and dwells in the third jhāna of which the noble ones declare: ‘He is equanimous, mindful, one who dwells happily.’

2. “Again, with the abandoning of pleasure and pain, and with the previous passing away of joy and dejection, he enters and dwells in the fourth jhāna, which is neither painful nor pleasant and includes the purification of mindfulness by equanimity.

So Right Concentration is simply concentration meditation, which should culminate in attaining the jhanas. It produces a wholesome state in which the mind is highly concentrated, purified, and refined. This state makes the mind ready to investigate of the nature of reality (dhamma vicaya), which is a factor of enlightenment and a path to the third stage: wisdom.

This makes a lot of sense, and in fact casts into doubt any method of practice that doesn't develop deep concentration and absorption before attempting a breakthrough of insight. I know these methods, called Dry Insight, are currently in vogue in Theravada, promoted by scholars who know the Canon far more better than I do, so I'd be curious to see how they justify contradicting this explicit teaching.

Stage 3: Wisdom (Prajñā)

1. “When his mind is thus concentrated, purified, bright, unblemished, rid of defilement, malleable, wieldy, steady, and attained to imperturbability, he directs it to knowledge of the recollection of past lives. He recollects his manifold past lives [...]

2. “When his mind is thus concentrated, purified, bright, unblemished, rid of defilement, malleable, wieldy, steady, and attained to imperturbability, he directs it to knowledge of the passing away and rebirth of beings. With the divine eye, which is purified and surpasses the human, he sees beings passing away and being reborn, inferior and superior, fair and ugly, fortunate and unfortunate. He understands how beings pass on according to their actions [...]

3. “When his mind is thus concentrated, purified, bright, unblemished, rid of defilement, malleable, wieldy, steady, and attained to imperturbability, he directs it to knowledge of the destruction of the taints. He understands as it really is: ‘This is suffering. This is the origin of suffering. This is the cessation of suffering. This is the way leading to the cessation of suffering.’ He understands as it really is: ‘These are the taints. This is the origin of the taints. This is the cessation of the taints. This is the way leading to the cessation of the taints.’

[...]

1. “When he knows and sees thus, his mind is liberated from the taint of sensual desire, from the taint of existence, and from the taint of ignorance. When it is liberated there comes the knowledge: ‘It is liberated.’ He understands: ‘Birth is destroyed, the spiritual life has been lived, what had to be done has been done, there is no more coming back to any state of being.’

No more commentary needed. What a beautiful sutta.