大般涅槃經義記 5.315

5.315

「以行分」下答第三難，前言見行多修慈悲、愛修喜捨，是故應二。佛今答之，行時有別，是故應四。「行分應四」總以標舉，「若行慈」下別以顯之。

From "in terms of practice, they are divided" onward answers the third objection. The earlier objection stated that those of view-practice mostly cultivate benevolence and compassion, while those of craving-practice cultivate sympathetic joy and equanimity, and therefore there should only be two. The Buddha now answers it: because there are differences at the time of practice, there should indeed be four. "In terms of practice, there should be four" generally sets forth the proposition; from "if one practices benevolence" onward, it demonstrates this specifically.