[C]hapter 16 is traditionally understood as showing that Shakyamuni is the Everlasting Original Buddha, and from that point of view, is regarded as the core of the second half of the Lotus Sutra. Since it does maintain the eternal life of Shakyamuni, such an interpretation certainly seems reasonable, but it is important to notice how that eternal life is taught.

The inception of the revelation of the everlasting life of Shakyamuni Buddha is in chapter 15, where a question is raised about the countless bodhisattvas who emerged from the earth and were said to have been taught from the remote past by Shakyamuni. Here at its inception, the teaching of the eternity of Shakyamuni Buddha is already related to bodhisattvas.

Thus, since I became Buddha a very long time has passed, a lifetime of innumerable countless eons of constantly living here and never entering extinction. Good sons, from the beginning I have practiced the bodhisattva way, and that life is not yet finished…

In short, unlimited, endless bodhisattva practice is used to demonstrate the eternal life of the Buddha.