大般涅槃經義記 5.316

5.316

「以無量故，亦得名四」，答第四難。向前難言無量應一，若言四種則非無量。佛今答之，良以具足四種無量，故得言四。

"Because they are immeasurable, they are also able to be called four" answers the fourth objection. The earlier objection stated that "immeasurable" should be one, and if one speaks of four kinds, then they are not immeasurable. The Buddha now answers it: truly because they are complete with four kinds of the immeasurable, one may speak of four.