大般涅槃經義記 5.325

5.325

問曰：前三益眾生心可須修習，後一是其背化之心，何勞修乎？釋言：若不修捨無量，是則前三雖能齊益，多先益親，後及其怨。又無捨心，益親心易，利怨心難，為除是過，故須修捨。又無空捨，前之三種便成愛見，故須修捨。眾生緣慈，修之如是。

Question: The former three minds that benefit sentient beings certainly need to be cultivated, but the latter one is a mind of turning away from transforming beings; why bother cultivating it? Explanation: If one does not cultivate the immeasurable of equanimity, then although the former three are able to benefit equally, one will mostly benefit dear ones first and only afterward reach adversaries. Furthermore, without the mind of equanimity, the mind to benefit dear ones arises easily, while the mind to profit adversaries is difficult; to eliminate this fault, one must cultivate equanimity. Furthermore, without empty equanimity, the former three become craving and views; therefore, one must cultivate equanimity. Cultivating benevolence taking sentient beings as objects is like this.