Nichiren Daishonin wrote this letter while he was in exile in Itō on the Izu Peninsula. It was addressed to Kudō Sakon-no-jō Yoshitaka, known also as Kudō Yoshitaka, the lord of Amatsu in Awa Province.
Kudō Yoshitaka is said to have converted to Nichiren Daishonin’s teachings around 1256, about the same time Shijō Kingo and Ikegami Munenaka did, a few years after the Daishonin first proclaimed his teachings. While the Daishonin was in exile on Izu, Yoshitaka sent offerings to him and continued to maintain pure faith. He was killed defending the Daishonin at the time of the Komatsubara Persecution in the eleventh month of 1264. The Four Debts of Gratitude is the only letter still extant that the Daishonin addressed to him.
In this letter, in light of the reason for his banishment, Nichiren Daishonin expresses his conviction that he is a true practitioner of the Lotus Sutra. He mentions the “two important matters” that concern his Izu Exile. He states, “One is that I feel immense joy,” and explains the reasons for his joy. The greater part of the letter consists of this explanation. Following this, he states, “The second of the two important matters is that I feel intense grief.” Citing passages from the Lotus and Great Collection sutras that reveal the gravity of the offense of slandering the Law and its devotees, the Daishonin explains that he grieves at the thought of the great karmic retribution his tormentors must undergo. This is the concluding part of the letter.
In the body of the letter, the Daishonin gives two reasons for his “immense joy.” One is that he has been able to prove himself to be the votary of the Lotus Sutra by fulfilling the Buddha’s prediction made in the sutra that its votary in the Latter Day of the Law will meet with persecution. The other reason is that, by suffering banishment for the sutra’s sake, he can repay the four debts of gratitude. He declares that the ruler who condemned him to exile is the very person to whom he is the most grateful; thanks to the ruler, he has been able to fulfill the words of the Lotus Sutra and so prove himself to be its true votary.
Then, the Daishonin stresses the importance of repaying the four debts of gratitude set forth in the Contemplation on the Mind-Ground Sutra. The four debts of gratitude are the debts owed to all living beings, to one’s father and mother, to one’s sovereign, and to the three treasures—the Buddha, the Law, and the Buddhist Order. Among these four debts of gratitude, the Daishonin places special emphasis on the debt owed to the three treasures, without which one could not attain Buddhahood.
https://www.nichirenlibrary.org/en/wnd-1/Content/6
