俱舍論記 23.48

23.48

「此四善根至一剎那故」者，釋第四句。此四善根依欲界身起，人、天九處，除北俱盧。唯依欲九身，以依彼身容入見道，彼是見道近眷屬故。餘不能入，故不依彼。前三善根三洲初起，後生天處亦續現前。第四善根天亦初起，一剎那故。又《婆沙》第七云「問：何故天中不能初起？答：彼處無勝厭離等作意故。問：惡趣中有勝厭離等作意，何故不起此善根耶？答：惡趣中無勝依身故。若有勝厭離等作意，亦有勝依身者，則能初起。此類善根，欲天中雖有勝依身，而無勝厭離等作意；惡趣中雖有勝厭離等作意，而無勝依身。人中具二，故能初起。」

Regarding 'These four roots of good... because of being a single moment': this explains the fourth pāda. These four roots of good arise relying on bodies of the desire realm, in nine places among humans and devas, excluding Uttarakuru. They rely solely on the nine bodies of the desire realm, because relying on those bodies one can enter the path of seeing, as they are proximate retinues of the path of seeing. In other bodies one cannot enter it, and thus they do not rely on them. The first three roots of good arise initially in the three continents; later, reborn in the heavenly realms, they also continue to become manifest. The fourth root of good also arises initially in the heavens, because it is of a single moment. Furthermore, the Vibhāṣā (fascicle 7) says: 'Question: Why can they not arise initially in the heavens? Answer: Because in that place there is no superior mental engagement of revulsion and so forth. Question: In the bad destinies there is superior mental engagement of revulsion and so forth; why do they not generate these roots of good? Answer: Because in the bad destinies there is no superior support-body. If one has both superior mental engagement of revulsion and so forth, and a superior support-body, then one is able to generate them initially. Regarding roots of good of this kind, although the desire-realm devas possess a superior support-body, they lack superior mental engagement of revulsion and so forth; although the bad destinies possess superior mental engagement of revulsion and so forth, they lack a superior support-body. In humans both are complete, and therefore they are able to generate them initially.'