妙法蓮華經玄贊 2.84

2.84

十三善巧方便，依此法門得成佛已，復為眾生說天人等五乘之法，成佛智慧巧方便故。

Thirteenth, "the Excellent Skillful Means": because having attained buddhahood in reliance on this Dharma gate, he further preaches the Dharma of the five vehicles, such as that of gods and humans, for sentient beings—a skillful means for accomplishing the Buddha's wisdom.