This may be meant to emphasize by implication that the teaching is uttered by one who has transcended the human condition, one beyond the otherwise endless cycle of rebirth and death, i.e. beyond dukkha.
The word's original significance is not known and there has been speculation about it since at least the time of Buddhaghosa, who gives eight interpretations of the word, each with different etymological support, in his commentary on the Digha Nikaya, the Sumangalavilasini:[2] Monks, in the world with its devas, Mara and Brahma, in this generation with its ascetics and brahmins, devas and humans, whatever is seen, heard, sensed and cognized, attained, searched into, pondered over by the mind—all that is fully understood by the Tathagata.
[4]: 381–382 Tathā means "thus" in Sanskrit and Pali, and Buddhist thought takes this to refer to what is called "reality as-it-is" (yathābhūta).
Another interpretation, proposed by the scholar Richard Gombrich, is based on the fact that, when used as a suffix in compounds, -gata will often lose its literal meaning and signifies instead "being".
[6] Shcherbatskoy gives the following example from the Mahabharata (Shantiparva, 181.22): "Just as the footprints of birds (flying) in the sky and fish (swimming) in water cannot be seen, Thus (tātha) is going (gati) of those who have realized the Truth."
[8]: 227 A tathāgata has abandoned that clinging to the skandhas (personality factors) that render citta (the mind) a bounded, measurable entity, and is instead "freed from being reckoned by" all or any of them, even in life.
[8]: 235 As Sariputta puts it, his questioner Yamaka "can't pin down the Tathagata as a truth or reality even in the present life.
"[9] These passages imply that condition of the arahant, both before and after parinirvana, lies beyond the domain where the descriptive powers of ordinary language are at home; that is, the world of the skandhas and the greed, hatred, and delusion that are "blown out" with nirvana.
A variety of similar passages make it clear that the metaphor "gone out, he cannot be defined" (atthangato so na pamanam eti) refers equally to liberation in life.
[11]: 95 In Sn 1074, it is stated that the sage cannot be "reckoned" because he is freed from the category "name" or, more generally, concepts.
[11]: 94 Nagarjuna expressed this understanding in the nirvana chapter of his Mulamadhyamakakarika: "It is not assumed that the Blessed One exists after death.
[12]In Vajrayana Buddhism, the Five Tathāgatas (pañcatathāgata) or Five Wisdom Tathāgatas (Chinese: 五智如来; pinyin: Wǔzhì Rúlái), the Five Great Buddhas, and the Five Jinas (Sanskrit for "conqueror" or "victor"), are emanations and representations of the five qualities of the Adi-Buddha or "first Buddha" Vairocana or Vajradhara, which is associated with the Dharmakāya.