妙法蓮華經玄義 4.69

4.69

四禪，用注雨三昧者，四禪如大地，具種種種子。若不得雨，芽不得生。一切善根，在四禪中，謂業種、三諦種。修諸行雨，自生三昧；慈悲應機，生他三昧（云云）。

For the fourth dhyāna, the raining-down samādhi is used: the fourth dhyāna is like the great earth, possessing all kinds of seeds. If it does not receive rain, sprouts cannot grow. All roots of goodness reside in the fourth dhyāna, meaning the seeds of karma and the seeds of the three truths. Cultivating the rain of various practices, he personally gives rise to the samādhi; responding to capacities with compassion, he gives rise to the samādhi in others, and so on.