Written in the fourth year of Kenji (1278), this letter is also referred to as Before and after Sado because it makes a clear distinction between the teachings the Daishonin expounded before his exile to Sado Island and those during and after his Sado exile. He compares the former to the pre-Lotus Sutra teachings, which Shakyamuni preached as an expedient to lead his disciples to the Lotus Sutra. Concerning his true teaching, the Daishonin says, “I secretly conveyed my teaching to my disciples from the province of Sado.” Quoting the Buddha’s words, he refers to that teaching simply as “this great Law.” More precisely, this teaching was explained in two of his most important writings, The Opening of the Eyes and The Object of Devotion for Observing the Mind.

The recipient of this letter is generally believed to be Misawa Kojirō, a lay follower of the Daishonin who was the lord of Misawa in Fuji District of Suruga Province, though some consider it given to Kojirō’s grandson, Masahiro.

Misawa appears to have kept his distance from the Daishonin for fear of antagonizing and arousing the suspicions of the Kamakura shogunate. But the Daishonin expresses understanding of his position as the lord of a manor responsible for a fief, family, and retainers, and kindly encourages him.

https://www.nichirenlibrary.org/en/wnd-1/Content/112