The Lotus Sutra is Buddha's heart embodied in written words

The Buddha's utterances have become the works that compose the entire body of sutras and bring benefit to all living beings. And among the sutras, the Lotus Sutra is a manifestation in writing of the Thus Come One Shakyamuni's intent; it is his voice set down in written words. Thus the Buddha's heart is embodied in these written words. To illustrate, it is like seeds that sprout, grow into plants, and produce rice. Thought the form of the rice changes, its essence remains the same. 17/12

From the Writings of Nichiren Daishonin
The Pure and Far-Reaching Voice