Nichiren Daishonin wrote this letter on the thirteenth day of the twelfth month of what is thought to have been 1276. The letter is a reply, it is generally believed, to Toki Jōnin, who had apparently written about a dream in which some danger to the Daishonin and his followers was revealed by the ten demon daughters.

After thanking Toki for the offering he had also sent, the Daishonin refers to the Buddhist principle that if one’s mind is strong, the protection of the deities Same Name and Same Birth, who are always with one, will also be firm. If this is so, he urges, how much truer must it be of the gods who protect the place of practice.

He also encourages Toki with a story from The Words and Phrases of the Lotus Sutra describing a thief who gained the golden head of a deity’s image simply by reciting the words “Namu Buddha,” or “Hail to the Buddha.”

The Daishonin points out that, in the light of this story, even though one may be guilty of faults, one may escape major difficulties if one is devoted to the three treasures of Buddhism.

Furthermore, he says that he views the divine instructions from the ten demon daughters as a sign that difficulties can be avoided and that good fortune is on its way.

And it is the Lotus Sutra, he emphasizes in conclusion, that allows one to change poison into medicine, difficulties into good fortune.

https://www.nichirenlibrary.org/en/wnd-2/Content/272