妙法蓮華經玄贊 5.302

5.302

The Commentary says: This corresponds to considering conversion through the causes of the Great Vehicle. The house has only one gate through which the bodhisattvas can emerge. If I were suddenly to bestow wisdom and supernatural penetrations and preach the great causes to transform the two sons, abandoning the expedient means of preaching the three vehicles, the vessels of the two vehicles would be small, unable to practice accordingly and attain deliverance from the myriad sufferings. Since the gate is narrow and small, they might fall back. This also implicitly corresponds to speaking of terrifying matters, so that they are not burned and harmed by the fire.