淨名經集解關中疏 1.182

1.182

四無量心是菩薩淨土。菩薩成佛時成就慈悲喜捨眾生來生其國　此慈悲喜捨也。肇曰。此四心周被無際故名無量也。此下雜就萬行明也。

"The four immeasurable minds are the bodhisattva's pure land; when the bodhisattva attains buddhahood, sentient beings who have perfected loving-kindness, compassion, sympathetic joy, and equanimity come to be born in his land." These are loving-kindness, compassion, sympathetic joy, and equanimity. Sengzhao says: "Because these four minds pervade everywhere without boundary, they are called 'immeasurable.' From here down, it is explained variously in terms of the myriad practices."