藥師經疏 1.33

1.33

經。以此善根至如來所者　三隨所願樂。今言以此善根者。是前持戒等善根。謂修此善根願生西方也。云何名為極樂世界稱讚。經說假使經於百千俱胝那庾多劫。以其無量百千俱胝那庾多舌。一一舌上出無量聲讚其功德。亦不能盡。是故名為極樂世界。梵音阿彌陀。此云無量壽。

Sūtra: With these roots of goodness […] to where the Tathāgata is. / Third, following what is aspired to and delighted in. Now, stating "with these roots of goodness" refers to the aforementioned roots of goodness such as upholding precepts; it means cultivating these roots of goodness with the wish to be born in the Western [Direction]. Why is it called the World of Ultimate Bliss? The praise in the sūtra says: Even if one were to pass through hundreds of thousands of koṭis of nayutas of kalpas, and with immeasurable hundreds of thousands of koṭis of nayutas of tongues, each tongue producing immeasurable sounds to praise its virtues, one could still never exhaust them. Therefore it is called the World of Ultimate Bliss. The Sanskrit sound is Amitābha; here it is translated as Immeasurable Life.