Nichiren Daishonin wrote this letter at Minobu in the last month of the fourth year of Kōan (1281) to the lay nun of Kubo, thanking her for the offerings that she had sent him. The lay nun was a widow who lived with her daughter in Kubo in Fuji District of Suruga Province, but little else is known about her. From the contents of the several letters addressed to her, she appears to have been a believer of pure faith who frequently sent offerings to the Daishonin.

In response to her gifts, the Daishonin compares making offerings for the sake of Buddhism to a way of planting “good roots” or accumulating merit and good fortune. In the opening passage, he explains that the benefit gained from donations depends upon the time, the place, and the person to whom they are offered. Moreover, even a large donation, if it derives from wealth obtained by harming or exploiting others, will never produce benefit, even though offered for the sake of Buddhism. Also, the Daishonin explains that one’s sincerity in making the offerings and the virtue of the person or teaching to which they are made are vital.

https://www.nichirenlibrary.org/en/wnd-1/Content/163