Over the my years reading the Lotus Sutra I’ve puzzled over why the Buddha predicts that when Śāriputra becomes the the Buddha Flower-Light he “will also lead the living beings [of his world] by the teaching of the Three Vehicles.” Why not just teach the Lotus Sutra? I dealt with this in detail back in early 2021 in my post Abiding in the One and Employing the Three. In Chinese Master Hsuan Hua’s commentary on Chapter 3, A Parable, he offers a succinct answer.
Hsuan Hua Lotus Sutra Commentary, v4, p38SUTRA
“Tathagata Flower Radiance shall also teach and transform living beings by means of the Three Vehicles. Śāriputra, when this Buddha appears in the world, although it will not be a troubled age, because of his past vows he shall teach the Dharma of the Three Vehicles.”
COMMENTARY
Tathagata Flower Radiance shall also teach and transform living beings by means of the Three Vehicles: Śrāvakas, Pratyekabuddhas, and Bodhisattvas. Śāriputra, when this Buddha appears in the world, although it will not be a troubled age characterized by the five turbidities, because of his past vows he shall teach the Dharma of the Three Vehicles. Why is that? In the past, he learned the Buddhadharma from Śākyamuni Buddha. Since his teacher taught the Dharma of the Three Vehicles, as his disciple, Śāriputra aspired to follow his teacher’s example. Therefore, even though he shall not be born in the troubled world of the five turbidities, he will nevertheless teach the expedient Dharma of the Three Vehicles.