大般涅槃經義記 5.301

5.301

三伴侶不同，故立四種。先就慈悲明相伴助，慈欲與樂，無悲除苦，樂則不生，故須修悲；悲欲拔苦，無慈與樂，苦則不去，故須修慈。是二相須，故須並修。次以喜心伴助前二，慈欲與樂，悲欲拔苦，若無喜心除其嫉妬，是則拔苦、與樂不勝，故須修喜。喜欲慶物，若無慈悲拔苦與樂，知何所慶？故修前二，是三相須，故須齊修。次以捨心伴助前三，前三雖欲拔苦、與樂、慶利眾生，若無捨心是則拔苦、與樂、慶物不得齊等，故須修捨。捨離欲等，若無前三拔苦、與樂、慶利眾生，知復就何以說平等？故修前三伴助後捨。又復前三是其有行，後一空行。若無空捨，是則前三便成愛見；若無前三，是則捨心於空滯沒。是四相須，故須並修。「是故名四」，總以結之。

Third, because their companion aids are different, four kinds are established. First, their mutual assistance is explained in terms of benevolence and compassion: benevolence desires to bestow happiness, but without compassion to remove suffering, happiness will not arise, so one must cultivate compassion; compassion desires to alleviate suffering, but without benevolence to bestow happiness, suffering will not depart, so one must cultivate benevolence. These two rely on each other, hence they must be cultivated together. Next, the mind of sympathetic joy accompanies and assists the former two: benevolence desires to bestow happiness and compassion desires to alleviate suffering, but without the mind of sympathetic joy to eliminate envy, the alleviation of suffering and bestowal of happiness will not be superior, so one must cultivate sympathetic joy. Sympathetic joy desires to rejoice with beings, but without benevolence and compassion to alleviate suffering and bestow happiness, what would there be to rejoice in? Therefore one cultivates the former two; these three rely on each other, so they must be cultivated equally. Next, the mind of equanimity accompanies and assists the former three: though the former three desire to alleviate suffering, bestow happiness, and rejoice in the benefit of sentient beings, without the mind of equanimity, the alleviation of suffering, bestowal of happiness, and rejoicing with beings cannot be equal, so one must cultivate equanimity. If one abandons desire and so forth through equanimity, but lacks the former three to alleviate suffering, bestow happiness, and rejoice in the benefit of sentient beings, on what basis could equality be spoken of? Therefore one cultivates the former three to accompany and assist the subsequent equanimity. Furthermore, the former three are practices of existence, while the last one is a practice of emptiness. Without the equanimity of emptiness, the former three would become attachment and views; without the former three, the mind of equanimity would sink and drown in emptiness. These four rely on each other, so they must be cultivated together. "Therefore they are called four" concludes this generally.