無量壽經優婆提舍願生偈註 1.18

1.18

These two lines are named the perfection of the merit of adorned shape and appearance. The reason why the Buddha originally gave rise to this adorned merit was that he saw that while the sun travels through the four quarters, its light does not cover the other three regions; while courtyard torches are in a residence, their illumination does not fill ten yards. For this reason, he gave rise to the vow for full, pure illumination, just as the luminous discs of the sun and moon fully complete their own substance. Although that Land of Peace and Bliss is vast and boundless, there is nowhere that its pure illumination does not pervade; hence it is said: "Its pure light is fully complete, / Like a mirror, or the discs of the sun and moon."