"...We see from the sutra that only these four bodhisattvas had been the disciples of Shakyamuni, the lord of teachings, since numberless major world system dust particle kalpas in the past; from the time he had first aroused the aspiration for and attained enlightenment, they had never followed any other Buddha, nor had they required the instruction of the theoretical and essential teachings.
Thus T’ien-t’ai says, 'The great assembly witnessed the Bodhisattvas of the Earth alone making this pledge.' He also states, “[The Buddha said of the Bodhisattvas of the Earth,] ‘These are my disciples, destined to propagate my Law.’ Miao-lo says, 'The children propagate the Law of the father.' And Tao-hsien states, “The Law embodied therein [in the Lotus Sutra] is the Law that was realized countless kalpas in the past, and therefore it was entrusted to persons who had been the Buddha’s disciples from countless kalpas in the past.' Thus these five characters of Myoho-renge-kyo were entrusted to these four bodhisattvas." (WND)
“It appears that these Four Bodhisattvas are the people who are the disciples of the Master of Teachings Lord Shakya since kalpas as many as the worlds touched or not by the dust particles of five hundred of tens of trillions of nayutas of assamkheyas of great trichiliocosms (gohyaku jinden go) and who also, from their first arising of the Bodhi Mind, have not adhered to other Buddhas and who have not yet made an appearance in the Two Doctrines [of the Manifestations and the Original]. Tendai says, “He only sees the issuing of vows from the direction below [the Earth]”. He also says, “These are My disciples; they should spread My Dharma” and so on. Myoraku says, “The child spreads the father's Dharma." Tao‑hsien says, “Since the Dharma is the Dharma of the One Who Attained Long Ago, therefore He assigns it to the people of the One Who Attained Long Ago." It is the Five Characters Myo Ho Ren Ge Kyo that He yields to these Four People.” (STN, v. 1, 783‑784 -- Lamont)