Chapter 12 tells about the future becoming a buddha of Devadatta, the extremely evil one who rebelled against Shakyamuni, and the sudden awakening of an eight-year-old dragon girl. This chapter has been revered since ancient times as an expression of the awakening of evil people and women. While the esoteric Shingon school often uses the term “becoming a buddha in one’s present” it was first used when Zhanran, the sixth patriarch of the Chinese Tiantai school, interpreted chapter 12. The chapter may have been inserted into the Lotus Sutra later and does not form a natural part of the narrative line of the sutra as a whole. Yet, for the reason mentioned above, it is still revered and recited.
Yoshiro Tamura, "Introduction to the Lotus Sutra", p77

[In chapter 11] there is the sudden appearance of the Treasure Stupa, the two buddhas sitting side by side, the gathering together of the buddhas who are embodiments or representatives of Shakyamuni, the united buddha-land, the purification of the Sahā world, and so on. These things were traditionally understood to imply that Shakyamuni Buddha is the Everlasting Original Buddha, and were taken to herald chapter 16, “The Life of the Tathagata.” But chapter 11 also teaches the propagation of bodhisattva practice, which is its ultimate purpose. We can see this in the following:

Who is able to teach the Wonderful Dharma Flower Sutra everywhere throughout this world? Now indeed is the time. Before long the Tathagata will enter nirvana. So that it will last forever, the Buddha wants to entrust this Wonderful Dharma Flower Sutra to someone.

Thus, it encourages actual bodhisattva practice in this world during the latter days and teaches the entrusting of the Dharma to such bodhisattvas.

It is implicit in chapter 11 that Shakyamuni both exists eternally and unifies the bodies of the various buddhas. The Treasure Stupa hangs in the air, with the two buddhas—Abundant Treasures and Shakyamuni— sitting in it side by side. Shakyamuni going to the seat in the Stupa in the air represents the infinite spatial extension of his world. Since Abundant Treasures Buddha is a previous form of Shakyamuni Buddha, their sitting side by side represents the infinite temporal extension of Shakyamuni’s existence. The various buddhas of the ten directions are embodiments of Shakyamuni, which indicates that the true body of Shakyamuni is manifested everywhere. The return to Shakyamuni of all of these embodiments of him as he enters the Stupa indicates that the worlds of the ten directions are unified into one buddha-land. This, too, is intended to reveal that Shakyamuni Buddha is a unifying Buddha.

In chapter 11, a jeweled Stupa rises up out of the ground and hangs in the air. Shakyamuni Buddha shifts his seat from Mt. Gṛdhrakūṭa to the jeweled Stupa in the air. Thus the scene changes from the meeting place on Mt. Gṛdhrakūṭa to the meeting place in the air. After chapter 22, the setting returns to Mt. Gṛdhrakūṭa. This has been called the “three meetings in two settings.”

The especially notable things in chapter 11 include the rising up out of the ground of a jeweled stupa, the two buddhas sitting side-by-side, the gathering together of Shakyamuni Buddha’s embodiment or representative buddhas, and the one universal buddha-land. … This chapter also teaches and explains the so-called “six difficult and nine easy practices” concerning the proclamation of the Lotus Sutra. Further, the verses at the end of the chapter, from “This sutra is so difficult to embrace . . .” up to the last phrase, . . . should receive offerings from all human and heavenly beings,” are known as “the phrases of difficulty in embracing the sutra,” or the “jeweled Stupa verses.” Even now people continue to recite them frequently.

In chapter 11, “The Sight of the Treasure Stupa,” a jeweled Stupa in which Abundant Treasures (Prabhūtaratna) Tathagata sits floats in midair. Shakyamuni Buddha goes from the ground to the Stupa in the air and sits beside Abundant Treasures Buddha. With that, the buddhas who are embodiments or representatives of Shakyamuni Buddha come from various directions to be united with him, while at the same time, various worlds are united into a single buddha-land. Abundant Treasures is a buddha who appeared prior to Shakyamuni. One can understand that the two of them sitting side-by-side symbolizes that Shakyamuni has been a buddha from the very remote past—that is, it suggests the universality of Shakyamuni Buddha. The gathering together of the buddhas embodying Shakyamuni from throughout the universe and the common buddha-land express the idea that Shakyamuni Buddha is a unifying buddha.

In this sense, chapter 11 should be taken as a kind of prelude to chapter 16, “Ihe Lifetime of the Tathagata.” As in chapter 16, this chapter also emphasizes bodhisattva practice, advocates actual bodhisattva practice in the heart of this Sahā world during the last days, and teaches entrusting the Dharma to bodhisattvas. Thus, we ought to reexamine ideas such as the jeweled Stupa rising up, the gathering together of buddha embodiments, and a common buddha-land from the perspective of promoting bodhisattva practice.