The Six Kinds of Arhat

T1606 explains "reflection" here in a specific, technical sense proper to this classical analysis: it refers to the arhat's readiness to actively end their own present existence, through the arhat's own spiritual power, rather than risk an actual retrogression from the fruit already attained — "having reflected" means having formed this specific readiness; "not having reflected" means not having formed it. On this account, the arhat prone to retrogression is so weak in faculty that even this readiness offers no protection at all — distraction alone, whether or not this readiness has been formed, is enough to cause the loss of their present dwelling in meditative happiness, referring specifically to the mundane dhyāna-level absorptions this dwelling rests on, not to arhatship's own underlying liberation from the contaminants, which every one of the six kinds shares alike and none of them ever loses. The arhat who guards through reflection stands one degree steadier: distraction alone is enough to cause loss only when this protective readiness has not been formed, but once it has been formed, that same distraction no longer succeeds in dislodging the present dwelling.

Each kind in this sequence stands one degree steadier than the one before it. The arhat who guards through vigilance no longer needs the special readiness to end their own existence in order to hold their attainment — simple ongoing vigilance against distraction is already sufficient — but distraction, once it does occur, is still enough to cause loss. The unshakable arhat has advanced further still: distraction itself no longer poses any threat at all, whether present or absent, and the present dwelling remains secure regardless. T1606 notes one specific limitation that still applies even here: this same unshakable arhat, despite this stability, remains unable to sharpen their own faculties — that is, unable to convert their still-dull faculties into sharp ones — a further capacity reserved for the kind examined next.

T1606 clarifies precisely what distinguishes this fifth kind from the unshakable arhat examined just before it: both share the very same stability against distraction, but only this fifth kind retains the further capacity to actually convert their own still-dull faculties into sharp ones, "sharpening the faculties" meaning exactly this conversion from a lower, dull faculty into a higher, sharp one. The sixth and final kind, unshakable by nature, requires no such conversion at all, since sharp faculties were already present from the very beginning rather than needing to be cultivated afterward — the same unshakable stability shared by the two kinds before it, but paired from the outset with sharp faculties rather than dull ones sharpened only later. Taken as a whole, these six kinds trace a single continuous progression: from an arhat whose attainment remains fully vulnerable to ordinary distraction, through several intermediate degrees of increasing security, to one whose attainment was never, from the very start, capable of being shaken at all.