Nichiren Daishonin wrote this letter in the second month of 1280 to Niike Saemon-no-jō, an official in the Kamakura shogunate. Niike was from Niike Village in Iwata District of Tōtōmi Province. He and his wife had been converted to the Daishonin’s teachings by Nikkō and had maintained their faith despite government pressure.

First, Nichiren Daishonin tells Niike what great fortune it is to have been born in the Latter Day of the Law with the mission to spread the correct teaching of Buddhism throughout the world. Yet it would be foolhardy to profess faith in the Lotus Sutra and then commit slander. The consequence is to descend into an evil path of existence, regardless of one’s role or status. Using the example of the cold-suffering bird, the Daishonin admonishes his believers never to lapse into negligence, or be tempted by fame or fortune.

After mentioning the deplorable state of the country and the degradation of Buddhist priests, he depicts the purpose of the Lotus Sutra by comparing an ordinary person to an egg. Like the fluids in an egg that develop into a bird, enlightenment exists as a potential within human life. Lastly, he says that the key to enlightenment is faith in the Gohonzon.

https://www.nichirenlibrary.org/en/wnd-1/Content/145