In ratana sutta, there’s a passage describing immersion in Nibbāna. (amataṁ vigayha)
Dedicated to Gotama’s dispensation,
Ye suppayuttā manasā daḷhena,
strong-minded, free of sense desire,
Nikkāmino gotamasāsanamhi;
they’ve attained the goal, plunged into freedom from death,
Te pattipattā amataṁ vigayha,
and enjoy the quenching they’ve freely gained.
Laddhā mudhā nibbutiṁ bhuñjamānā; Variant: nibbutiṁ → nibbuti (mr)
This sublime gem is in the Saṅgha:
Idampi saṅghe ratanaṁ paṇītaṁ,
by this truth, may you be well!
Etena saccena suvatthi hotu.
There’s immediately 2 possibilities for this: either cessation of perception and feelings, which in MN59, has been hinted as the highest happiness, but not explicitly stated as such, MN 59: Bahuvedanīyasutta—Bhikkhu Sujato (suttacentral.net) or the perception of nibbāna itself, which seems to be limited to only arahants, as stream winner like Ānanda didn’t knew about it. AN 10.7: Sāriputtasutta—Bhikkhu Sujato (suttacentral.net)
Points for the first possibility is that it’s also what we and orthodox theravada would regard as parinibbāna, just that it’s temporary, so plunging into nibbāna seems apt to have cessation, also it’s implied to be the highest happiness, which is usually just reserved for Nibbāna. Points against it is that non-returners can also attain it and it seems contradictory to the ratana sutta requirement of those who has reached the goal. And the ratana sutta said freely gained, whereas the cessation of perception and feeling seems to be not available for arahants who are wisdom liberated, that is without formless attainments.
Points for the second one is that it seems to fit that only arahants has it and it’s freely gained, but it’s a bit open to whether it’s considered higher happiness than cessation. Philosophically speaking it’s quite hard to beat no feelings as the highest happiness. Or if we drop the unstated requirement for this plunging into the deathless as the highest happiness, we can fit this.
Thoughts? What does commentaries say about it?
PS. or is it just ending of greed, hatered and delusion, so arahants are always plunged into Nibbāna, even when they experience physical pain.