妙法蓮華經玄義 7.49

7.49

四、約體用明本迹者，由昔最初修行契理，證於法身為本，初得法身本故，即體起應身之用，由於應身得顯法身；本迹雖殊，不思議一。文云：「吾從成佛已來，甚大久遠若斯，但以方便教化眾生，作如此說。」

Fourth, clarifying the original source and the traces in terms of substance and function: through originally cultivating practice and tallying with the principle, realizing the dharma-kāya is the original source. Because the original source of the dharma-kāya was first attained, from the substance arises the function of the response body; because of the response body, the dharma-kāya is able to be revealed. Although original source and traces are distinct, they are an inconceivable unity. The text says: "Since I attained buddhahood, it has been extremely long and distant like this; yet through expedient means to teach and transform sentient beings, I made such statements."