The Lotus Sūtra, fascicle 2, the 3rd chapter on “A Parable” states:
“He who does not put faith in this sūtra and slanders it, [will commit the sin of exterminating the seed of Buddhahood in all the people in the whole world. Or, suppose those who frown at and harbor doubt about the teaching of this sūtra . . . despise, hold in contempt, hate, envy, and bear a deep grudge against those who read, recite, copy, and uphold this sūtra. What would such people get in return? You should listen carefully.] Such people will fall into the Hell of Incessant Suffering upon death, [where their suffering will last endlessly, for a kalpa after another…, until they fall into the world of beasts becoming a huge serpent as long as 500 yojana in length.]”
The same sūtra, fascicle 7, the 20th chapter on the “Never Despising Bodhisattva” also asserts: “[Some of the four categories of Buddhists (monks, nuns, laymen and laywomen) had impure minds. They got angry, spoke ill of him, saying, ‘Where did this ignorant monk come from?’ They struck him with a stick, a piece of wood, a piece of tile or a stone.] They were tormented in the Hell of Incessant Suffering for as long as 1,000 kalpa for the sin of persecuting a practicer of the Lotus Sūtra.”
The Nirvana Sūtra, too, declares: “If one avoids good teachers who preach the True Dharma and instead takes refuge in false dharmas, one will sink into the Hell of Incessant Sufferings, undergoing all the sufferings with his huge body of 84,000 square yojana.”
Examining many sūtras, we thus see they all regard slandering the True Dharma the most serious crime. How sad it is that people [in Japan] all should wander out of the gate of the True Dharma into the prison of evil dharma! Such ignorance is causing everyone [in Japan, high and low,] to be pulled by the rope of evil teachings and caught forever by the net of slandering the True Dharma! In this life such wanderers are lost in the mist of delusions; in the next life they will sink to the bottom of flaming hell. How sad it is! How terrible it is!
You should promptly discard your false faith and take up the true and sole teaching of the Lotus Sūtra at once. Then this triple world of the unenlightened will all become Buddha lands. Will Buddha lands ever decay? All the worlds in the universe will become Pure Lands. Will Pure Lands ever be destroyed? When our country does not decay and the world is not destroyed, our bodies will be safe and our hearts tranquil. Believe these words and revere them!
Risshō Ankoku-ron, Treatise on Spreading Peace Throughout the Country by Establishing the True Dharma, Writings of Nichiren Shōnin, Doctrine 1, Pages 141-142