Devadatta was the Buddha’s cousin and nemesis. After going forth together with several other relatives of the Buddha (Kd 17:1.4.1), his initial success in meditation was corrupted by his desire for gains and fame (SN 17.35). He tried to take over the Saṅgha but was denounced by the Buddha. His attempt to create a schismatic faction failed and he died in disgrace.

The Chinese parallel at EA 43.4 says that this discourse was given during the time he was being lavishly supported by Prince Ajātasattu (SN 17.36, Kd 17:2.1.1).

Compare the “noble quest” on MN 26 and the search for a “bull elephant” in MN 27. In each case the metaphor emphasizes the specific and uncompromising nature of the goal. The moral is to not stop until the journey is truly complete.

While “knowledge and vision” (ñāṇadassana) that is “in accordance with reality” (yathābhūta) refers to the vision of the four noble truths at stream-entry, “knowledge and vision” by itself does not have a well established technical meaning. At DN 2:83.1 it is said to be a vision of the body with its consciousness, although this passage is rare and in MN 77:29.11 is not described as “knowledge and vision”. Elsewhere it is used in a variety of senses for a kind of clear and enhanced spiritual understanding.

The “irreversible freedom” (asamaya, literally “not temporary”) is that of arahantship, as opposed to the “temporary freedom” of samādhi, from which one can fall away due to bad conduct (AN 5.149), like Devadatta. | Text inconsistently has vimokkha (“liberation”) here and vimutti (“freedom”) in the next line, although elsewhere the suttas always read vimutti. It seems that when these attainments came to be included in the Vimokkha Chapter of the Paṭisambhidāmagga (a late canonical Abhidhamma-style text), they were renamed vimokkha to fit the context (Ps 1.5:2.10). The commentary then cited that passage here using vimokkha, but the commentarial gloss must have contaminated the text. I translate under the assumption that the correct reading is vimutti, although it makes no practical difference.

This links the “irreversible” freedom with the “unshakable” freedom of arahantship; the two are equated at MN 122:4.1.