妙法蓮華經玄義 6.166

6.166

是神通來，非神通生。是應來，非應生。是大誓願相關，非願生。是因緣相召，如下方聞聲、妙音見光，是諸佛大事業來，非業生。業生者，不能業來；業來，非是業生。願通生者，不能願通來；願通來者，亦能願通生，亦能應來。應來，亦能應生（云云）。

These are supernormal arrivals, not supernormal births. They are responsive arrivals, not responsive births. They are connected through great vows, not volitional births. They are summoned by causes and conditions, as those below hear the sound and Gadgadasvara sees the light; they come for the great work of the buddhas, not as retributive births. Those of retributive birth cannot come through retributive arrival; retributive arrival is not retributive birth. Those of volitional and supernormal birth cannot come through volitional and supernormal arrival; those who come through volitional and supernormal arrival can also undergo volitional and supernormal birth, and can also come through response. Those who come through response can also undergo responsive birth (and so on).