無量壽經優婆提舍願生偈註 2.10

2.10

門者入出義也，如人得門則入出無礙。前四念是入安樂淨土門，後一念是出慈悲教化門。

'Gate' has the meaning of entering and exiting, just as when a person finds a gate, entering and exiting are unobstructed. The first four [gates of] mindfulness are gates for entering the Pure Land of Peace and Bliss; the last one [gate of] mindfulness is the gate for exiting to teach and transform with compassion.