Why the Buddha is said to have taught in this way is illuminated by the social context of the time in which he lived. The Buddha was a Srama?a, a wandering ascetic whose "aim was to discover the truth and attain happiness." He is said to have achieved this aim while under a bodhi tree near the River Neranjana; the Four Noble Truths are a formulation of his understanding of the nature of "suffering", the fundamental cause of all suffering, the escape from suffering, and what effort a person can go to so that they themselves can "attain happiness."
These truths are not expressed as a hypothesis or tentative idea, rather the Buddha says:
“ These Four Noble Truths, monks, are actual, unerring, not otherwise. Therefore, they are called noble truths. ”
The Buddha says that he taught them...
“ ...because it is beneficial, it belongs to the fundamentals of the holy life, it leads to disenchantment, to dispassion, to cessation of suffering, to peace, to direct knowledge, to enlightenment, to Nirvana. That is why I have declared it. ”
This teaching was the basis of the Buddha's first discourse after his enlightenment. In early Buddhism this is the most advanced teaching in the Buddha's Gradual Training.
 Pali canon text
The Nature of Suffering (Dukkha):
"Now this ... is the noble truth of suffering: birth is suffering, aging is suffering, illness is suffering, death is suffering; sorrow, lamentation, pain, grief and despair are suffering; union with what is displeasing is suffering; separation from what is pleasing is suffering; not to get what one wants is suffering; in brief, the five aggregates subject to clinging are suffering."
Suffering's Origin (Samudaya):
"Now this ... is the noble truth of the origin of suffering: it is this craving which leads to renewed existence, accompanied by delight and lust, seeking delight here and there, that is, craving for sensual pleasures, craving for existence, craving for extermination."
Suffering's Cessation (Nirodha):
"Now this ... is the noble truth of the cessation of suffering: it is the remainderless fading away and cessation of that same craving, the giving up and relinquishing of it, freedom from it, nonreliance on it."
The Way (Marga) Leading to the Cessation of Suffering:
"Now this ... is the noble truth of the way leading to the cessation of suffering: it is the Noble Eightfold Path; that is, right view, right intention, right speech, right action, right livelihood, right effort, right mindfulness, right concentration."
 Mahayana understanding of the Four Noble Truths
Certain major Mahayana sutras, including the Mahaparinirvana Sutra and the Angulimaliya Sutra, present variant versions of the Four Noble Truths of the Buddha:
the Truth of Suffering relates to the failure to recognize the eternity of the Buddha;
the Truth of the Cause of Suffering concerns the perversion and distortion of the True Dharma (i.e. wrongly insisting that the Buddha and Dharma are impermanent);
the Truth of the Cessation of Suffering relates to the correct meditative cultivation of the tathagatagarbha (indwelling Buddha Nature in all beings) and not erroneously viewing it as non-Self and empty; cessation of suffering also arises with the elimination of inner defilements, when one can then enter into the Buddhic Essence within oneself: "When the afflictions have been eradicated, then one will perceive entry into the tathagata-garbha";
the Truth of the Path to the Cessation of Suffering entails envisioning the Buddha, Dharma and Sangha as eternal, unshakable and indestructible. (Mahayana Mahaparinirvana Sutra, tr. by Kosho Yamamoto, ed. by Dr. Tony Page, Nirvana Publications, London, 1999-2000)
The Angulimaliya Sutra similarly emphasises the seeing and knowing of the Buddha's eternality, immutability and peace as the key factors in liberation from suffering; failure to see this eternal nature of ultimate reality is said to constitute the primary cause of beings' continued entrapment in the sufferings of samsara.
It should be noted that this view is specific to certain Mahayana schools, most notably the Tathagatagarbha and Jonangpa traditions. The ideas that the Buddha and his Dharma are eternal and that one's inner Buddhanature is not empty would be denied in other Buddhist traditions such as Madhyamaka and Zen.