” Since you now appear certain to attain Buddhahood, perhaps the heavenly devil and evil spirits1 are using illness to try to intimidate you. Life in this world is limited. Never be even the least bit afraid!
And you demons, by making this man suffer, are you trying to swallow a sword point first, or embrace a raging fire, or become the archenemy of the Buddhas of the ten directions in the three existences? How terrible this will be for you! Should you not cure this man’s illness immediately, act rather as his protectors, and escape from the grievous sufferings that are the lot of demons? If you fail to do so, will you not have your heads broken into seven pieces in this life2 and fall into the great hell of incessant suffering in your next life! Consider it deeply. Consider it. If you ignore my words, you will certainly regret it later.”
This letter was written at Minobu to Nanjō Shichirō Jirō, commonly known as Nanjō Tokimitsu, in the second month, 1282, when he was gravely unwell. At the time of writing this letter Nichiren Daishonin himself was seriously ill. The letter is traditionally called The Proof of the Lotus Sutra because it points out that all the Buddhas gave credence to the truth of the Lotus Sutra. However, it is also known as Prayer for a Return to Life from Fatal Illness because Tokimitsu was then battling a serious illness.
Nichiren explains to his disciple that as he, following his mentor, steadily moves on the path of enlightenment, devilish functions are bound to put obstacles on his way. He encourages Tokimitsu to not be afraid and continue on his path. The Daishonin then directly addresses the so-called demons, or negative workings in life. He sternly admonishes them for inflicting suffering on the disciple of a votary of the Lotus Sutra, warning that in doing so they risk making enemies of all the Buddhas throughout the ten directions and three existences. His words deeply and powerfully convey his towering spirit and conviction as a votary who has triumphed over great obstacles in his efforts to widely propagate the Mystic Law in the Latter Day. When the disciple strives with the same spirit as the mentor, there is no obstacle or devilish function that cannot be surmounted, and there is no illness that cannot be positively transformed in accord with the principle of “changing poison into medicine”. “The Proof of the Lotus Sutra” highlights the key to good health and long life and conveys the victory of mentor and disciple.