法華玄論 9.47

9.47

答：就事言之，一集一變則昧不覺土曠佛多，今令覺知佛多土曠故三集三變也。又諸佛常用三事，如三試等。又有所表者，以心垢土穢、心淨故土淨，三根眾生心垢應淨故三變土也。

Answer: Speaking in terms of events: gathering once and transforming once would leave people obscured and unaware that the lands are vast and the buddhas are numerous; now, to make them realize that the buddhas are numerous and the lands are vast, he gathered three times and transformed three times. Furthermore, all buddhas frequently employ threefold matters, such as the three testings and the like. In terms of what is signified: because when the mind is defiled the land is impure, and when the mind is pure the land is pure, the mental defilements of sentient beings of the three faculties ought to be purified, hence the lands are transformed three times.