妙法蓮華經玄贊 5.264

5.264

贊曰：此釋所以。「匱乏」盡也。以此一乘假使遍授一佛國土五道眾生，有性、無性、定、不定姓，尚不匱乏，何況唯與有大乘性及不定種姓佛之真子，恐不足耶？

The Commentary says: This explains the reason. "Lacking" means exhausted. Even if this Single Vehicle were universally bestowed upon the sentient beings of the five destinies across an entire buddha-realm—those with the nature, without the nature, of determinate, or of indeterminate gotra—it would still not be exhausted, so how could there be fear of insufficiency when giving it only to the true sons of the Buddha who possess the Great Vehicle nature and the indeterminate gotra?