Let us go back for a moment to the Stupa of Treasures. Ordinarily a Stupa is a mausoleum where the relics (ashes) of Sakyamuni are enshrined. Once Sakyamuni is extinct, living beings can worship him only in his relics. The Sutra says that Many-Treasures Buddha will appear whenever and wherever the Lotus Sutra is expounded. This means that the living Sakyamuni, represented by his relics, and the Lotus Sutra are united as one single entity.
Introduction to the Lotus Sutra