法華義疏 9.138

9.138

此經明唯有一乘無有餘乘，一切眾生並皆成佛故悉與佛記，亦是悉與佛記則顯唯有一乘，故舉授記釋成一乘也。

This sūtra clarifies that there is only the one vehicle and no other vehicle; all sentient beings will equally become Buddhas, and therefore all are granted the Buddha-prophecy. It is also that by granting all of them Buddha-prophecy, it demonstrates that there is only the one vehicle. Therefore, conferring prophecy is adduced to explain and establish the one vehicle.