What is difficult to believe and difficult to understand about the Lotus Sutra?

“To put it briefly, all the doctrines possessed by the Thus Come One [name], all the freely exercised supernatural powers of the Thus Come One [function], the storehouse of all the secret essentials of the Thus Come One [essence], all the most profound matters of the Thus Come One [quality] —all these are proclaimed, revealed, and clearly expounded in this sutra [teaching].” - Lotus Sutra Chapter 21, The Transcendent Powers of the Tathagata (Buddha)