法華論疏 2.115

2.115

前是三慧，今是證慧。證慧者，是修慧後分始證得真如法身，故言增長功德心。

The previous were the three wisdoms; this is the wisdom of realization. The wisdom of realization refers to the later portion of the wisdom of cultivation, in which one begins to realize and attain the dharmakāya of thusness; therefore it is called "the mind of increasing merit".