Five Ways the Non-Returner Attains Final Nirvāṇa

T1606 clarifies the subtle distinction behind "the fetter that generates rebirth" and "the fetter that causes further arising": the active afflictive force that would actually drive a being onward toward taking a new rebirth-existence has, in every one of these three cases, already been exhausted, but the residual underlying tendency that still causes the aggregates to continue arising in sequence after death — dormant rather than actively operating — has not yet been fully exhausted. Following the Seven Fine Men Sūtra, these three variants are distinguished purely by timing, measured against how far a being has progressed toward the next existence at the moment the noble path finally manifests and burns away this last remaining tendency: in the very first variant, this happens the instant the intermediate state itself first arises, before any movement toward the next existence has even begun; in the second, it happens the instant reflection first turns toward that next existence, already somewhat underway; and in the third, it happens only once that movement has been sustained for some time, right at the final threshold, just before the next existence is actually reached. In every case, the crucial point is the same: final nirvāṇa is reached entirely within the intermediate state itself, never requiring the next rebirth to actually occur at all.

Where the previous three variants all reach final nirvāṇa before ever completing rebirth into the form realm, this pair — and the general case preceding it — waits until that rebirth has actually occurred. "Without further effort" means that the very power of habits already thoroughly cultivated in previous lives is sufficient for the uncontaminated noble path to manifest spontaneously, requiring no additional deliberate exertion at all once that rebirth has taken place. "Through further effort" is simply the opposite case: the very same rebirth has occurred, but the noble path manifests only once further deliberate exertion is actually applied. Both variants share the same starting point — full rebirth into the form realm, with neither fetter yet severed at the moment of that rebirth — differing only in whether the final push toward liberation still requires effort or arises entirely on its own.

T1606 distinguishes two distinct routes within this final variant, sorted by how deeply attached a practitioner remains to the taste of meditative experience itself. One who continues to savor the distinct flavor of each successive dhyāna along the way takes rebirth in every single level in careful sequence, from the very first form heaven all the way through to the highest, only reaching final nirvāṇa once that last and highest level has actually been reached. One who instead cultivates the fourth dhyāna without mixing in that same lingering attachment to lower flavors, bypassing the five pure abodes reserved for non-returners, presses onward level by level all the way to the very peak of existence itself before final nirvāṇa is reached there instead. And for those who do take the more gradual route through the five pure abodes specifically, T1606 explains that it is the very grade of mixed cultivation of the fourth dhyāna itself — mild through utmost-strong — that determines which of the five pure abodes, in matching order, becomes the destination of rebirth: the finer the mixed cultivation, the more refined the corresponding abode reached.