大毘盧遮那成佛經疏 13.61

13.61

甘露者，智智之別名。能除身心熱惱，得而服之不老不死，可以喻於如來之智也。今以此智除一切眾生熱惱，令得常壽之身。此甘露味亦從佛心生也。次如來腰印。亦准如來鉤作之，內風指而舒水指為異耳。此水指不須屈第三節也，是右手水指也。真言歸命如前。

'Amṛta' is an alternate name for the wisdom of wisdom (sarvajñajñāna). It can eliminate the feverish afflictions of body and mind; if one obtains and drinks it, one does not age or die, and it can serve as a metaphor for the Tathāgata's wisdom. Now, by means of this wisdom, one removes the feverish afflictions of all sentient beings, causing them to attain a body of eternal life. This taste of amṛta is also born from the Buddha's heart. Next is the Tathāgata's Waist Seal. It is also formed based on the Tathāgata's hook, differing only in tucking the wind finger inside and extending the water finger. This water finger does not need to be bent at the third joint; it is the right water finger. The homage of the mantra is as before.